Welcome, Jimster.
What fun to explore into Russian Simonovs - and you have a couple!
That's a good question. My guesstimate for production is Izhevsk's are maybe one in... ten? fifteen? twenty? compared to Tula's production. But Izhevsk's are far less often available for sale here. Folks find them and hold on to them, so the ratio difference on sites like Gunbroker will be even greater.
Am happy to be corrected. Anyone else have an opinion?
One part of the reason is they were made there for only two dated years compared with the nine or so years at Tula (dated + letter years). But another reason might be the difference in SKS production levels outright at those two arsenals; the military's demand fell on Izhevsk for their AK production at the same time. Finally, importers in different countries may have acquired different batches of Russian SKS's for sale, and that may have resulted in different percentages for us and, say, for Canada.
Congrats on having a matching Izhevsk. It is pretty rare and getting more so, and I hope you treat it well.
Care to post some pictures?