What can I make a baking form from?
With such tiny details, wood will give you trouble - even with very careful seasoning and greasing you will probably not be able to get the cake to release properly and without ripping the details apart. 

My first suggestion would be stoneware / clay:
You can easily shape it including details and after being glazed and burned it will be ready to use. Either find a potter do do it for you (even modeling it off a positive shape you supply) or do it yourself, you just have to find a kiln you can use.

Shaped stoneware molds have been in use for centuries, here are two random examples showing rather fine details:




Or find someone who can make it in metal, but your sheets must be a) thick enough to allow for thinning at the imprints and b) made to resist warping - that's definetively a job for a professional.