There are many sources but what I know of is in North America. Not sure about sources on mainland Europe. It also depends on what material you intend to use. Personally I like horn which would be period correct but there are many others. For ideas you can look at Maggard's for one.
https://maggardrazors.com/search?q=scales
They have a wide selection of premade scale and raw materials to make your own.
There is also Griffith's Shaving Goods.
https://www.griffithshavinggoods.com...oduct&q=Scales
They also have both premade scales and blanks.
Another source I use for horn and bone is guitar parts and more.
https://guitarpartsandmore.com/
They only have materials though so that would apply only if you want to make your own.
Of course these are all in North America as stated but perhaps they ship overseas. You can also find razor blanks and scale material on EBay.