It should be no problem. Avgas available at EKVG, BIEG, BIRK, BIKF, BGKK, BGBW,BGGH, BGSF, CYFB. Though it's always wise to call them and check. I guess the Daks to Normandy guzzled quite a bit of their stock on the round trip!
If you don't have HF you may have to route north of the Gander OCA e.g. BGSF to CYFB goes through the Nuuk FIR.
Frobisher Bay avgas is sold by the drum for about CAD$310 (50 US galls). In Greenland they transfer the drums to a bowser, so you just buy what you need (budget about 14 USD/gall).
Longest distance between Avgas stops is about 540NM (Iqaluit to Schefferville) though they may have a few drums at Kuujuaq
No special permissions required if you are flying with a standard CofA and no ferry tanking.
Make sure you have the correct visa for the US. VWP doesn't work for private flights).
Order your US customs decal in advance, though you can pay on arrival, but it may take a while to do.
Make sure you are registered with EAPIS and filed before entering the US.