You could try
Singers Asset Finance which, I understand, recently got back into aviation so may offer more flexible terms, but tread carefully!! Buying a helicopter is the easy bit; selling one is much more difficult, especially if it's a distressed sale because you couldn't afford the maintenance/running costs. You need to always be prepared to fund those inevitable 'unscheduled maintenance' items which, even on a 22, can easily run into many £000s. Why not try a syndicate? Or first negotiate a leaseback deal with a school (tread even more carefully!)? That might influence your buying criteria. Whatever you do, I hope it works out - let us know!