Eddie - Should be easy for you to get some decent, matched current production 6550s. For current production, I'd probably go with Kevin Deal at Upscale or Jim McShane.
just fyi - Kevin MIGHT have an issue with selling to you if he knows it's for ARC gear. Seems like I saw something or other about that on his site at one point. I don't recall what his problem with ARC was. It might have had something to do with biasing ARC gear. Check out his site.
Jim McShane enjoys a very good reputation and while I've yet to buy from him, I would if the need arose. He is very good with email replies but is just coming back from an illness so might be a little slow due to back log. You might consider contacting him to see what he has to say.
If you want to follow the safest course, why not buy them from ARC? Supposedly they are extremely rigorous with their tube screening procedures. They will charge a premium over what you can pay elsewhere. Assuming they aren't asking 5 or 10x more and since you only need two tubes, spending the extra $ for the "peace of mind" might be best.
Good luck.
