I was lucky enough to buy a battery powered filter air fed mask cheap off ebay. Although it's no good for spraying purposes I adapted it to feed air into the welding mask. I think maybe one of those air bed inflating pumps (with a suitable filter) or something similar could be rigged up.
get the best fit you can, if it's still to large, then put them through the washing machine... they'll shrink nicely !!. well at least mine did when they were in my back pocket of my boiler suit...
I'd reckon they were down to the next size down at least. Might be worth a try.
