This bookstore in Canada used to carry these bumper stickers in various sizes, and as far as is known, still does:
Daugavas Vanagu Bookstore (or as it's know in English: Latvian Bookstore),
phone 416-757-1482 (closed mondays and tuesdays).
address: 4 Credit Union Drive, Toronto, Ontario M4A 2N8
email:
latvianbookstore@latviancentre.org
p.s. they do take credit cards now.