If your in the states, I think you should try Vintage Productions. They are easy to deal with. No problems for me when I've ordered.
http://www.vintageproductions.com/shop/index.php?target=products&product_id=2613
What kind of blue nylon are you working on? Your best bet when it comes to making an authentic patched jacket is to find a period photo and replicate that on your jacket. Photos of blue nylon jackets patched in SAC are difficult to find. The only one I've come across that I can remember is this one which was taken in late 50s or very early 60s, when the L-2A was a rare sight.
A good source is with simple google searches. I think most SAC units didn't start using patches heavily until the introduction of sage green nylon. Just remember, the SAC shield patch was not worn until well after the retirement of blue nylon. I've seen people sell original blue nylon with a SAC shield patch which is a clear indication the patch was not original to the jacket. It's especially clear when they use a repro patch. :roll:
When it comes to the patches themselves, I think it depends if your patching an original jacket or repro. If your patching an original jacket then I'd say it's almost a must to use original patches. Some originals can be had for dirt cheap. Some can get VERY expensive. If using a repro jacket, then you can find some decent repro patches, but I'd still favor a cheaper original patch on a good repro jacket.
Hope I didn't confuse you. Let me know if you have any other questions. Good luck.