Hi @Patchworkmum I got one a while back that I've never ended up wearing. I have infusions and blood tests every month and just ask them to use the side that I didn't have nodes removed from. The only time I won't be able to do that is in an emergency and in that situation, I'll risk some lymphedema for life saving treatment.
If you are still interested, there are companies out there making them. A quick google will find someone easily enough. Mine is pink and says "ALERT. Axillary lymph nodes this arm. No blood pressure or needles". It's made by Mediband and I think it cost me about $10.