Ahoy modelbuilder,
I have heard but cannot confirm that either Yankee modelworks or
Nautilus models is working on a conversion for this u-boat, to
convert it to a type VII-C/41 which has the extended wintergarten and
lots of armament.
You could also try scratchbuilding. And in as far as armament goes,
the Revell Schnellboot S-100 could provide the following:
37mm(Flak 36) cannon
20mm(Flak 38) AA
20mm AA double barreled machine gun
Hasegawa makes an 8 ton German half track , you can borrow the beautiful
Quad 20mm AA from this kit to add to the u-boat.
Have a nice day and happy modeling.