So, letter frequency in Burns looks to be within shooting distance of letter frequency in English, could probably play with a standard set, around ten extra apostrophe tiles would be ideal, lacking that, I've generated a preliminary lexicon from a Project Gutenberg etext of the Poems & Songs of Robert Burns (etext #1279) stripped of Gutenberg boilerplate & glossary which omits the apostrophes. You can get that here. This is merely a handy reference guide, challenges should still be adjudicated by reference to the nearest copy of the works of Burns. Also it's machine-generated & I've haven't yet proofread it, so your mileage may vary.