Good afternoon
my country is France and i am new on this forum ,i have a shiloh with marking on the barrel 44-90 in my country impossible to found brass in this caliber ,i have tried in your country but when i found the caliber the seller do not ship in my county.So if a member know where i can bought or how to make this from another caliber i will be happy thank you
The best bet you might have getting brass for that is going with Bertram which is made in Australia. There is no one, with the demise of Jamison brass, at this time in the US making properly head stamped brass for the 44-90 or the 44-77 other than one or two custom brass makers that lathe turn cases, but again you will be up against the export problem.
You can trim and fire form brass from 45-100 or 45-110 brass, but there again availability will be a problem unless you can access some Norma brass. The 45 based cases are a little small in the rim but will still extract alright, and it will swell the web a bit but once fire formed lasts a good long time.
With the proper swaging equipment it is possible to form it from 348 winchester but the hardness of that brass doesn't work real well with blackpowder loads.