Thanks for all the info Fred and Mike. It's good to hear a comparison from folks that have experience with all the options. The Wilburs shock from Europe looks interesting. Not sure what the exchange rate is from dollars to euros, but they look expensive and you have to deal with shipping and customs from across the pond.
I can't find a Progressive Suspensions 465-series (part # 465-1155B) shock in stock anywhere (this is what Murph's sold). I found several sites that had it listed as being in stock, but after I called or emailed them, I found out they were not available. The manufacturer probably discontinued the model that fits the C-10.
The C-14 shock from the second generation Concours seems like the next best shock for the C-10 when you rummage through the used parts bin. But, the main problem for me is that the shock is too tall for the C-10 and the Soupy lowering links interfere with the external spring. Even when you can find the Soucy link (also discontinued), the bike would still be taller than what I have now (1.5" lower than stock). Ted says the Soucy link puts the C-14 shock right at stock height, that would put me back on my tiptoes.
That leaves the ZZR1200 shock (which is what I decided to get). The ZZR1200 is readily available and cheap. While about a 1/4" taller than stock, but with lowered forks and a low profile 17" rear tire, my bike would still be about 1/2" lower than stock (without Soupy's lowering links). I have looked at as many photos as possible showing the installed ZZR1200 shock on a Concours 1000. It appears to me that my Soupy's lowering links will work with some minor tweaking. If not, once I get a lower seat, I should be back to flat-footing it again.
About the only downside to the ZZR1200 shock I've heard is the spring rate is a little light (but still better than stock). I weigh in at 190 lbs. and plan to get lighter weight mufflers and battery, so perhaps the springs will be tolerable. Again, it's still better than a working stock shock and as a reminder, my current shock leaks, so anything will be better than what I currently have now. I found a low mileage ZZR1200 shock that I ordered for $75.
SHORT VERSION: The Progressive 465-series shock is unavailable and C-14 shock is too tall. So, I bought a ZZR1200 shock instead.