Try looking for one in a Junkyard. That's really not a "collector" truck yet, and that particular part isn't likely to fail, so it makes sense nobody is re-making it.
What exactly is wrong with yours?
FWIW, if that's the old white dial style, you can also swap in a needle style from a slightly newer truck. I think any cluster assembly from '88-94 should fit, and the needle-style clusters came online in the early 90's IIRC...
Looks like there are several on EBAY, but you'd probably get a slightly better deal at a junkyard...
Good Luck!!