Afternoon all!
I've been searching for an interior set for a 76mm Sherman. However, I've only been able to find interior sets for the 75mm version. Does anyone know of a good interior set for a 76mm Sherman Turret on an M4A1? I'd really appreciate any help.

I don't think there is one. I remember looking for one with no joy.

I know this is a 2 year old post, but I figure if I found it, someone else may be helped along in their search as well.

There are no kits for 76mm Sherman turret interior...but, and it's a big but, there are ways around this. I would recommend getting lots of good references to help you with knowing how the wet stowage actually looked:

The book M4 Sherman at War by James D. Brown and Michael Green
contains some excellent information on how the breech of the gun, the bottom of the turret basket, and the stowage looks.

There is another book, I can't remember the title, though it was at my local hobby shop, it was part of a series on tank manuals or reconstruction manuals...something like that - anyway, if I ever find it, I'll be sure to add to this post. That book had the breakdown of blueprints for every Sherman variant there was with detailed blueprints of the turret basket bottoms. However I tried to scratchbuild the bottom based on the M4 Sherman at War book and it came out well (but I abandoned the project since I was trying to make a Firefly basket bottom only to realize they didn't have one (the left side of the basket is simply cut off on the Fireflies, but I digress).

Once you've got the references, there are some kit options to keep scratchbuilding to a minimum. First of all, Italeri's old Sherman contains the breech for the 76mm wet stowage Sherman (it's pretty basic, but checks out with what the book shows, so you could use it). https://images-na.ssl-images-amazon.com/images/I/91D3XmhZovL._SX355_.jpg

It is misnamed as an M4A1 without mention of the 76

Then I'd recommend the CMK kit for most of the turret (once again check references, as I am not as well informed in the wet stowage shermans) but you'll basically have to use the right side with the commander's seat and the gunner's seat (those and all controls were the same), the scratchbuild the bottom of the basket. Not sure about the ammo stowage in the turret itself, since the rounds were considerably longer and just a millimeter thicker in those tanks - check references again.

As for the lower stowage (under the turret) there are no kits available at all.