Bondo is a 3M brand of automotive body filler so you likely won't find a direct translation. Most North American hardware stores carry it but in Europe it may be a bit harder to come across. Check to see if you have Isopon or U-Pol at a store local to you.
Also since you're new to the forums you may not have noticed but this thread hasn't been touched in about eight years. Best practice is to let old threads stay buried unless you have some really valuable information to revive the thread. This keeps all the current information more visible. There's a few good Bondo tutorials in the
Pepakura Build Sticky Index if you need some help with your build!