If you were reading a newspaper on the 29th December 1808, underneath the months old news from the New York papers on "Mr Jefferson's message, that the American ministers at London and Paris were instructed to make to the governments of Great Britain and France propositions on the subject of the American embargo.", you would often find this advertisement appearing for the first time:

"To be had of TREWMAN and SON, Exeter.
This day is published
In 25 vols. royal 18mo. embellished with engravings, price 6l.16s.6d. and on fine paper with portraits, and proof impressions of the plates, price 13l. extra boards,
THE BRITISH THEATRE, or a COLLECTION OF PLAYS, which are acted at the Theatres Royal Drury-Lane, Covent-Garden and Haymarket, printed under the authority and by permission of the managers, from the prompt books.
With BIOGRAPHICAL and CRITICAL REMARKS
By Mrs. INCHBALD.
Printed for Longman, Hurst, Rees, and Orme, Paternoster-row; and sold by Trewman and Son, or E. Upham, J. Penny, and G.Dyer, Exeter; Haydon and Co. and Rees and Curtis, Plymouth; L. Congdon, Dock; and all booksellers in town and country.
List of plays, contained in this work, which are sold separately, price 1s. each.
Mountaineers. Speed the Plough. Wheel of Fortune.Lovers Vows. Inkle and Yarico. Isabella. Wild Oats. Douglas. Stranger. Country Girl. Dramatist. Hamlet. Grecian Daughter. Busy Body. John bull. Tancred and Segismunda. All in the Wrong. Macbeth. Bold Stroke for a Wife. Poor Gentleman. Such Things are. Oroonoko. Love in a village. Road to Ruin. Jane Shore. Clandestine Marriage. Edward the Black Prince. Merry Wifes of Windsor. Rule a Wife and have a Wife. Mourning Bride. Cure for the Heart Ache. All for Love. Way to keep him. King John. She Stoops to Conquer. Conscious Lovers. Revenge. Love for Love. Every Man in his Humour. Coriolanus. Jew. Romeo and Juliet. Careless Husband. George Barnwell. Beaux' Stratagem. Gustavus Vasa. West Indian. Julius Caesar. Every one has his Fault. Jealous Wife. Tempest. Orphan. Cato. Belles Stratagem. Zara. Fair Penitent. Deserted Daughter. First Love. Siege of Damascus. Provoked Wife. Rival Queens. Lady Jane Grey. Love makes a Man. Roman Father. Point of Honour. Barbarossa. Merchant of Venice. Wives as they Were. King Lear. Constant couple. School of Reform. To Marry or not to Marry. King Henry VIII. King Henry V. Good Natur'd Man. Antony and Cleopatra. Recruiting Officer. Countess of Salisbury. Winters Tale. De Monsort. Court of Narbonne. Castle of Andalusia. Suspicious Husband. Bold Stroke for a Husband. New Way to pay old Debts. Way to get Married. Fatal Curiosity. Earl of Warwick. Fontainbleau. Honey-moon. Wonder. Lionel and Clarissa. Earl of Essex. King Henry IV. Part I, Brothers, a Comedy. She Would and She Would Not. Inconstant. The Rivals. Measure for Measure. Know your own Mind. King Richard III. King Henry IV. Part 2. Gamester. Man of the World. Maid of the Mill. Duenna. Provok'd Husband. Chances. Distressed Mother. Beggar's Opera. Mahomet. Foundling. As You Like it. Twelfth Night. Much Ado about Nothing. Cymbeline. Venice Preserved. Comedy of Errors. Tamerlane. Surrender of Calais. Battle of Hexham. Iron Chest. Heir at Law. Othello. Heiress.
In the course of January will be published,
A COLLECTION of FARCES and other After-pieces, in 7 volumes, forming a supplement to the above work.
This collection will include, besides the old stock of after-pieces, the most popular Modern ones, the copy-rights of which are the sole property of the publishers of this work."

Except for Sheridan's School for Scandal, all the plays mentioned in MP are listed in this ad (Thomas Morton wrote "School of Reform"). Even if it was not this publication the players were consulting (and if it was, Sir Thomas must have purchased the 25 volumes in absentia, and the discussion must have taken place in September 1809 at the earliest), still it shows that, as Myretta said, obtaining unbound copies of Lovers Vows was as simple as ordering it from any bookshop and paying a shilling apiece.

There is a lot of humour hidden in the discussion of plays to act- Hamlet, Othello and Macbeth have wonderful parts for women, Maria and Julia want tragedy, but not as an Othelia or Gertrude to Henry's Hamlet! I can see that Macbeth suffers a surfeit of witches, but with Mrs Norris as Hecate ... I don't dare make any more casting suggestions but still I think they could have managed it.
Tom is quoting from the Gamester "My name is Norval; on the Grampian Hills/ My father feeds his flocks; a frugal swain,/ Whose constant cares were to increas his store."
Mary appears all obliging, but the Duenna is a comic opera, and she just happens to have a beautiful singing voice and a preference for comedy.
There is also a political aspect to Tragedy v Comedy: only theatres with patents from the King were allowed to perform Tragedy, but musical entertainments, could be played elsewhere - another example of Mary portrayed as the Opposition?