You might contact any retailer that sells to the auto A/C businesses in your area. If there are none you might have to make up such a sticker yourself.

I can see where there may not be such stickers out there since what you have done is so rare, but the information is rather vital to anyone working on your A/C system.

I would get two of these stickers and put one one the radiator support and one on the compressor where it could not be missed.