Thanks for the tips/suggestions guys. Some more background on the situation.
I think it was a specific workout that caused the problem, so I don't think it's an ongoing/degenerative thing. As for getting inserts, we have neither that store chain up here Kev, nor would it be open at the moment anyway. Another contributing factor is I walk around barefoot (or in socks) 80% of the time. I've been working from home for 10 years or so, so wearing shoes isn't common (at best) and a rarity (at worst). I've dug out pair of Nike's that I used to wear while working out that have good arch supports in them, and have been trying to wear those all day. It seems to be helping (along with doing various stretches recommended by the interwebz). It's not constant pain, just hits if I over extend the motion of a calf stretch. It's (naturally) worse in the morning after being immobile, but by the end of the day is almost non-existent.
So, I'll try and dig up some old Dr. Scholl's inserts to put in my regular workout shoes and see if that helps, and continue to stretch it out.