Nanco Nancy Rhode Island Novelty makes prize-only plushes for arcades & fairs. Here's a fairly large size Knuckles plush that apparently never got made. It can be found at their site (for a while) but then is always marked "unavailable". This may just be a prototype they made & then…
Pajamas These are also available in the UK. The design is not painted on at all, rather it's dyed in there for sleeping comfort. There should be a Sonic on the pants somewhere, but Gear doesn't own this. Sizes are unknown.