Direwolf20 was having the same problem on his current Server Play YouTube episodes. Keep in mind the Forge server is running mostly pre-release mods for testing to get them ready for release... He may see a solution long before we do.
At issue is the idea that some packs that used to generate certain ores either are not yet ready for 1.10.x for whatever reason, or some that used to generate ores no longer do so. I believe Tinkers Construct is in this second category.
I used to make Aluminum Brass for tool forms but, like you, cannot find aluminum. Luckily we can make single use forms using clay and cobble, for example, an Axe head (2 cobble lost, 2 clay lost by default recipe):
1). Make the part using cobble.
2). Melt 2 clay in the smelter... As the clay hardens on the part that part is lost.
3). Use the clay form to make say an Iron Axe Head. This time the form is lost.
A good thing about this change is that with 1.10 Clay became part of Vanilla WorldGen and is nowhere near difficult to find.
I've heard that several mods like IC2(?) have recipes for replacements for some missing ores but that requires a whole new infrastructure to be built.