Someone already gave the best answer for 24 hole tremolo harmonicas. RUMC in England had a set of 12 tremolo harmonicas (one each key) in a box. They are now about 86lbs British Sterling or about $122 USD plus a fee to convert about 6 or 7 dollars from USD to BPS. These peopel may also be found on Ebay. Super people and you can pay with paypal. The harmonicas are SWAN INCONCEIVABAL models and they are unbelievable professional quality instruments. Vented covers plastic combs and good strong brass reeds. Tuning is precise and the resonance is to dye for... I've been playing tremolo harmonicas for a few years now... about 50 and these are really unbelievable... I hope that you find them a treat to play...

Rayzor