Ive gathered some field maple seeds from finer leaved local trees. There are plenty around in any woody area.
Not sure how many of the seeds will prove to be viable. I guess about 5% of the gathered ones. i cut a few of the seeds in half - most were empty - but a very few had a green kernel in them.
i guess if all else fails i will go to the local instant hedges nursery for some 60-80cm seedlings of hawthorn and field maple.
Ive got the seeds wrapped up in moist cloth - il see if any hatch after a few days. hopefully i get at least 2 viable ones.