Here ya go >>>
Bilstein 24-186476.
Not finding mine anywhere local, I bought off Amazon.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
You can also buy them from rvchassisparts.com which is Spartan's site. They ship quick, I've bought several items from there.
I'm sure you can get this crossed to Koni if you want, some say they ride better (I have no opinion on that).
Lastly, when you search for parts for this front end, it's made by Reyco-Granning and is model Tuthill IFS1200. Searching for parts under the actual manufacturer instead of Spartan IFS 1200 usually yields more results. I was able to save several hundred dollars buying ball joints from Reyco-Granning instead of through Spartan.
Here is a link to the downloadable repair manual >>>
https://reycogranning.com/rg/wp-cont...-1320-1370.pdf
Good Luck !