Look at Chrysler, DeSoto, Dodge, and Plymouth cars from the late 40's thru early 50's. The 3.73 differential gears was an option in all of the Mopar vehicles, but those would be your best bets to find something. You'll have to do some digging to find the stamping on the top of the differential housing to know what gears are inside.
I got lucky to find the 3.73 diff that I currently have in my truck. There was a forum member here, many years ago, that put up a post regarding an axle that he bought. He was looking for a 4.10 diff to use in his '53 Suburban, which he used to pull a boat, or camper trailer, and it had an OD transmission. He purchased an axle from a '50 Plymouth thinking it would have 4.10 gears. It turned out it had the 3.73 gears. At the time I happened to have an extra truck axle with 4.10 gears, so I sent him a message about doing a diff assembly swap. I offered to ship my 4.10 diff to him and it he would ship his 3.73 diff back to me. After some picture trading we decided the only difference was the drive flange, as the driveshafts are different between the cars and trucks. I pulled the drive flange off of the pinion, crated it up, and shipped it to him on my dime. It was exactly what he needed so he put his 3.73 diff back in the crate and shipped it to me. I replaced the pinion seal and reinstalled the drive flange. It was a direct replacement into my axle.
I've heard that sometime in the early 50's ('52 or '53) there was a change in the spline count for the axle shafts and side gears. However, some here have reported having good luck in swapping the side gears in the differential to correct that mismatch.