Carsten, did you get that pretty black one that looked un-used on Ebay the other night? It's a gorgeous lens but it will require a large front panel to mount on. They were intended and are at home on the old studio cameras with 9X9 inch lens boards. Mine is mounted on a 6 3/4" board that fits into a 9X9 Ilexpo shutter and it's maxed on that board. They won't go on a 6X6 board.
As to mention on line, the Dallmeyer 3A (16 inch) patent petzval is sort of the jumping off place to the really big lenses. The 4A is a magnitude bigger than anything common so simple rarity probably answers your question. There may have been 100 3A's for every 4A but that's a rank guess.
As to use, the sky's the limit. Or maybe the bellows is the limit. If you wad through the stuff at my site long enough you'll eventually find some things shot with a Dallmeyer 4A. Gorgeous lens.