These trees are usually grafted, so any seed which is produced may be sterile, or will give a completely different form of maple, one you don't necessarily want. Some seeds require stratification before sowing, others can be sown in a cold frame in autumn.

Acer seeds are not produced at the tips of the leaves, could we have a photo please.

I'm assuming he/she means from pedicels towards the end of the stem with leaves on, Moongrower...

Possibly, would still like to see a photo though.