Those are so nice!
Canada Post has been including self adhesive letter seals when you buy a booklet of stamps the last years. Most of them are rather smallish. I like the bigger ones like these which were included in a stationary pack with themed paper and envelopes to go with the pet stamps (2004?)
I imagine that the King George VI era (which had lots of ciderella stamps) had some used for letter seals also.

Ah, I just realized, you probably mean just officially printed stamps meant for use as a letter seal. Hmmm.
Is there any with cats on them? Lions? Or as part of the wax seal impression? That would be neat.
The two new Canada 2010 Year of the Tiger stamps (Jam 8) are of a hand sealing-stamp carved as a tiger and the other postage stamp is the impression (in gold leaf) left when the seal was pressed into wax or paper (a stylized tiger, similar to heraldry). Sorry for image quality (borrowed from
ebay, not issued yet.)
