Originally posted by Karon:

IIRC you can upgrade the forge to level 6 with the materials you get up to the swamp biome

There are six upgrades for the Forge. Only 2 of them are available in the same biome level as the one that the Forge becomes available at (Black Forest). The other 4 all require materials from the next biome up (Swamp).

Likewise, the Workbench has 4 upgrades, only 2 of which can be made from materials in the same biome that that Workbench is first available at (Meadows). 1 of the remaining upgrades requires materials from one biome up (Black Forest) and the other requires materials from three biomes up (Iron from Swamp and Obsidian from Mountain).

There is already plenty of precedence to warrant waiting for more biomes to be developed before the Black Forge gets more upgrades. It only first becomes available at Mistlands, making Mistlands the low level base biome.

Be patient, or use mods - those are your only reasonable options at the moment.