While you may be able to find many parts from various suppliers (I'm in the US, so know nothing about EU suppliers,) you will end up finding that they are not quite right for your application.
If you want to build custom machinery (which robots are included in) in metal, then you have to learn to use a mill and a lathe! (Or a CNC mill and CNC lathe :-)
If you want to build custom machinery in plastics, then you probably ought to learn to use a 3D printer.