I am also looking for something about 12" wide by 24" long by 24" deep or so. Some combination of dimension that gives me a 20 gallon buffer for my laundry discharge.
I have a small laundry room with 1 1/2 drain service with no 2" drain service nearby and that may be OP issue as well meaning I cannot use a standpipe but wish to reconfigure my laundry room and recover space from my huge sink.
The only prefabs I can find are 18" or more wide and no good for me, and those are not deep so they are marginal in capacity for this second floor install, I would much rather have 20 to 22 gallon capacity instead of the 15 gallon in those 18" and not very deep tubs.
I am looking and looking and cant find any including from restaurant supply etc