Ok... I know there are a thousand places you could order stuff, and I hesitate to give any advice about where I've gotten stuff since I've been beaten up a little in the past for giving U.S. companies and somewhat more expensive answers. (didn't know they were more expensive

) But since no one else has stepped up yet, maybe this will be helpful or at least provoke someone into giving you closer/cheaper answers.
I have used The Michigan Toy Soldier Company for getting sculpting stuff before. They are very nice people, willing to answer questions, seem to have a good amount of materials, and ship internationally.
Main page:
https://www.michtoy.com/
Sculpting supplies:
https://www.michtoy.com/MTSCnewSite/supp ... pting.html
For scenery stuff, I've ordered straight from Woodland Scenics. Nothing like going to the source to make certain they have everything in stock (my problems with local dealers is that they never have the exact color of something I want, etc.), and they ship internationally, too. They have also been really nice when I've had questions.
Home page:
https://www.woodlandscenics.com/
Maybe this will help.