That's a common problem on any of the 150s of that particular vintage, up to, but not including, the L-model when it was changed. Every single one I've ever seen has cracked in the past, (and still is) or has been repaired. Usually, they look horrible.
Years ago, someone on the forum posted a picture of a new metal one from Cessna. You may want to check with Cessna's parts network and see if they're still available. (I just checked Hill Aircraft's online query, see below...)
Globe Fiberglass
used to sell a fiberglass version for a short time, but they're no longer in their online catalog. A quick call to Kevin @ Globe, revealed they did sell them at one time, from an individual who was making them for Globe. As of now, the mold
does exist, but it's not in Globe's posession and they're not planning on re-tooling another mold, nor selling them in the future.
Hope you're sitting down:
0452002-6 --
CAP NOSE
In Stock -- $2,244.00 $2,244.00
(Probably, guaranteed to crack again)
Sounds like a good business opportunity for a retired guy.