The SigWx does show tops (FL100+) but they are usually way off.
That's why a "cloud tops metar" would be great.
One can get it (as tephigrams) from two American university websites that carry worldwide baloon ascent data but this happens only at 0000Z & 1200Z - of some use for a daytime flight but limited to very stable air masses.
Bookworm - do you have a URL?