Four years back I wanted to pick up a Russian visa enroute. I found that there were certain consulates which were doing this, and many which were not. Russian consulates were, at that time, operating semi-independently, like little fiefdoms--making their own rules.
The rumored easiest place to pick up a visa was Tallin. I got my letter of introduction straightened out beforehand (using a visa service), but by the time I got to Tallin on my bike some sort of diplomatic crisis had erupted between my country and Russia. Instead of a few days, they told me it would take a month...and it was already almost October. I decided to bypass Russia.
The folks with the most reliable, up to date information on all of this were the visa agency I used for the LOI. I can't remember which one it was, but if you google Russian visa (or something similar), you'll find the several big ones which can do stuff on-line. It'll cost you, and you really want to know where you'll need to go for the visa itself, and what the current odds are.
Hope that's helpful.