[MadMax]

Cha chinggg! It's actually a bit of a rare thing to actually find the direct cause of an obscure problem via online diagnosis.

Unfortunately your spring is not a commonly sold item. They don't break and they don't get lost often so there is little aftermarket supply of them. If you're handy with model building you could wind your own spring from piano wire from the hobby store. Failing that look for alternatives at a place like Active Surplus. Also look for wierd coincidences. Maybe a mag spring has a similar diameter to your spring so you could trim a bit off of a mag spring to use as a reed valve spring.

More fuel for my burning distaste for clone shops that duplicate stuff without really appreciating the intent behind a design...

If you have a friend in the States who can bounce stuff for you, try mcmastercarr.com or smallparts.com (SP ships to Canada).

Both carry a lot of springs and bits and may have something close to what you need. You need a spring of similar diameter and helix angle (lead) and wire gauge. Your replacement will have to reduce any one of these: wire gauge, free length, lower lead in order to exert less force on your reed valve. Failing that, try modifying your existing spring.