Ahhh, gotcha. A quick 10-minute search doesn’t return anything promising. Most don’t support CAA, and even ones that are explicitly for checking CAA records fail to distinguish between NOERROR and SERVFAIL responses.
I don’t yet have the bandwidth to reliably host something myself (my servers are temporarily running out of my home for now until I can get them moved back into a datacenter - my last one jacked up prices. 
) but I’ll try and write my own web-based one instead of making it a Python script to distribute that someone could put…somewhere.