Check Prosphora seals. org Bread Stamps - they have an excellent selection of stamps (seals). I suggest the Russian Old Rite Stamp, which is very beautiful and makes lovely prosphora.
The same web site also has lots of information on baking altar bread.
Fr. Serge
I believe it's:
www.prosphora.org [
prosphora.org]
This is the site where I buy the seals for our church. We've been very happy with their quality. (I ordered 5 seals, and Fr George threw in an extra one for free!)
There are 5 of us (3 women, 2 men) at St Melany's who rotate the baking. It's worked out quite nicely.