Does anyone have
any suggestions for sources for this kind of thing?

For what its worth: I have a C5 OTA and a Pronto. I have solar filters for
both. In general I prefer the Pronto for most things, but for solar viewing, I
like the C-5.

Consider springing for a solar filter for the C-5.

Of course if the Ranger's filter is a Coronado or similar filter, then things
change but you could still probably fabricate a mount that would allow you to
view with the C5 through the Ranger filter.

jon