Charity shops are a favourite hunting ground for me and they are a great source of cheap music if you are prepared to spend time going through the sheet music racks. Amnesty Bookshop and Oxfam Art and Music are very good, though Oxfam can be quite pricey its all for a good cause. Although there is a growing body of music for mandolin there is much to be gained from browsing through violin music, tutor and exam books. These turn up regularly in my local Amnesty book shop, where they have a very well organised music section, and are instantly adaptable for mandolin. You will need to replace bowing markings for appropriate plectrum strokes but apart from that there is a huge choice for the adaptable mandolin player.
I recently picked up a complete scales and arpeggios grades 1 – 5, a scale syllabus to grade 8, a very old, but fascinating, mandolin method which I hadn’t seen before which had some useful exercises. A few weeks ago I found a Hummel mandolin sonata and there are often plenty of compendiums of popular tunes to expand your repertoire.
Its also worth looking at music for flute and recorders as these are also within the mandolin’s range. I’ve found some great 4 part arrangements some of which I’ve adapted for my mandolin ensemble. Most shops charge about £1.00 per sheet or maybe £2.00 for a book, and if you buy several at once will usually give a discount. Its also great fun because you can find things to play you might not have considered if you were paying full price. This way if you don’t like a piece when you get it home and play, it hasn’t cost much and you’ve donated to a good cause so you can feel good any way. Its a win win.