Here is a hard-to-find double slate sink, with drain boards. Note there is deep side and a shallow side. The drainboards were added so they need to be trimmed to fit your space. LooLoo has other slate drainboards that can be adapted for this sink.
Overall dimensions are 94″ x 21. The deep basin is 22″ wide and x 12″ deep and the shallow basin is 29″ wide and 6″ deep. The splash back is 11″ above the drainboard.
The sink is in excellent condition. As noted, the drain boards were added and one has been repaired. A sink like this is hard to find, however, making some adjustments is well worth the effort.