Bad news, the preheat American Fluorescent MS series, as seen here, here, and here, has been discontinued.  I ordered a few advertised as having magnetic ballasts and they did not.  I called the company and they confirmed that they are no longer being manufactured.  Now I'm deciding whether to keep them, return them, or try to retrofit them.  My preference would be to return them for the preheat version, but because they are a specialty item, most retailers order them directly from the manufacturer.  The only good news is they could theoretically be converted to preheat.  The fixture dimensions have not changed.  The fixtures are still U.S. made, but the new ballasts were made in China, while the magnetic ballasts they used before were also U.S. made.

In order to convert these, it looks like I would need Robertson L48 ballasts and starter sockets.

You can go to semperlite.com to find the ballast and starter sockets I got some stuff from them the prices were not bad.

I've gotten a few American Fluorescent strip lights.  I like the fixtures, but in all honesty, the ballasts they came with were crap, even the magnetic ones.  The best thing about them was the ability to go and replace the ballast with what I felt was a better one.  All the single lamp ones had starter knockouts, even if they came with electronic ballasts.  I currently have 4 AF fixtures installed.  A 36" strip that originally came with an electronic ballast, and now has an HPF magnetic rapid start ballast.  A 48" under cabinet fixture that originally came with one of those rubbish single lamp shop light ballasts.  It now has an Advance preheat F40 ballast.  Finally, a pair of 24" under cabinet fixtures that originally had Chinese preheat ballasts with poor ballast factor.  Those have been replaced with Advance ballasts with better BF. 

I found some NOS preheat fixtures on ebay. Check out my posting.

Those look nice.  I searched eBay for similar fixtures before I purchased the new AF strips.  If the seller hadn't misspelled "fluorescent", I probably would have found them.

Those look nice.  I searched eBay for similar fixtures before I purchased the new AF strips.  If the seller hadn't misspelled "fluorescent", I probably would have found them.

I agree. Sometimes I randomly search with words that are commonly misspelled to see what comes up and have found many things that way.

I've found this site to useful when finding some misspelled items on eBay.

I put new ballasts in my fixtures.  I ended up spending more time and money on these then I was planning to, but it was fun to retrofit them.