If you go to a Stihl dealer that makes chain loops from a reel .325 pitch in 0.050 gague has been the 3690 code or what you ask for in the first sentence. I think it is probably 3 years ago the product code for .325x.050 changed from the stuff with the necked down drive links. Initially Stihl made loops in Husky sizes like 72dl, now They have their own bars and seem to have stuck with their loop sizes. To make .325 loops now out of Stihl chain the preset tie straps are different for 0.050 and 0.063 because the drive link width or maybe thickness is different, chances of them using the wrong ones are significant.
Use the 3690 in a search on ebay. It is there. As for the reels see a Stihl dealer keep in mind the Oregon and Husqvarna nearest product is maybe $420 a roll from the lowest price seller.
3690 005 0078 is the code off a box I have for a 78 dl loop. You should be able to order from a Stihl place the loop you want just modify the last digit.