I don't know about that particular nerve block and where to get it, however there is a little known, very effective, noninvasive treatment for CRPS called Calmare Scrambler Therapy. It's very effective for neuropathic pain. Here's an article that talks about its use for CRPS: https://www.paintreatmentdirectory.com/posts/calmare-scrambler-therapy-is-an-effective-therapy-for-complex-regional-pain-syndrome-crps