I have plenty of junkyards near by and I want to upgrade to posi if possible.
Know any trucks and or cars I could look for one in? Maybe a Durango or dakota, older cars It's a 73 360 Charger at one.
1980 D150 SL6
8 1/4 3.55

8 1/4" sure grip rear ends have been around since the very late 60's...

You will most likely find them in ex-cop cars (80's Gran Fury/Diplomat), but occasionally found in other Mopars (you have to pull the cover and look for the spring pack in the center section).

You may find one occasionally in early-mid 90's Dakotas, Rams... but you are limited by year... so anything after 1997 you would need some new 29 spline axle shafts to work with the spiders. (Also some Dakota's can come with a 7 1/4" rear... count the bolts and look at the shape of the rear cover...)

That being said... there were lots of 1970's-1990's Trucks made with sure grip 9 1/4" rear ends (had one in 3.55 under my 92 Ramcharger), that would bolt under your truck without having to do all the fuss of changing the center out of the 8 1/4"), the only worry with that swap is making sure the bolt pattern matches what's in your truck....

I found my sure-grip 8.25 in a '74 Valiant but I don't know if it was original to the car. It had 11" drums on it, so maybe it came from a cop car or taxi? Gear ratio was/is 2.71.