Personally, I'd say just sell the ones you now have and aren't using, and buy those which you can.
I used adapters for a good long while at one end of my RCA MIT Magnum's as they entered into my balanced preamp at the time to very good effect. Thereafter on a SE preamp with as good results... my source through all that time was SE only.
Another thought is simply send them to Cardas for retermination. This action might be the more viable solution for you especially if you bought them new, as you know better what you have with them. if bought preowned, sell 'em and get those you need, you may even make money on the process!
If you need adapters on one end only I'd say get the adapters preowned for $40 or $50 per pr. and be done... but two sets puts you a lot closer to the price for retermination instead, though it'll likely be more for that.
I did that too. had some XLR cables bought new and got them redone to RCA. Going down to RCA from XLR is better, easier, and way more doable than the other way 'round. you keep one added conductor that way and it's usually saved for use as the common lead. The factory told me following the fix/redo the cables will actually perform better than a standard SE/RCA cable. Not having another likewise set to compare with, I took their word. Regardless, I was very well pleased.
As you are dealing with a signal strength that is variable, unlike that of coax (TV) cable, the apparent loss of signal strength is negligible using a set of adapters.
I kept that balanced amp longer than the preamp, and used adapters on the amps inputs as RCA wires were all I had at that time. the resultant sound was great.
Sometimes looking at things in a more practical light than that of the neurotic audiophile who fears loss of anything, or degredation of any sort, audible or not, is a very viable path to take. Especially if you have no mo' dough at the time to spend on a thing. Sometimes.... even if you do...