I love the design by me software, but there are too few LEGO Technic pieces.
Do you know somes places (in Europe) where I can find LEGO Technic pieces without buying sets ?
I'll pretend I didn't read the "without bying sets" part.
Go buy some!
Seriously, this is the simplest way to acquire good packs of assorted Technic parts, and if you haven't got much experience with Technic yet, building the models is a great way to learn.
Of course, some models are better than others in terms of assortment provided , but I don't know for sure what's the best value for money at the moment. Whether you want electric or pneumatic parts will play a role, as will possible clearances in your area.
If you can find a LEGO education reseller, they also carry Technic parts packs, but BrickLink is probably going to be cheaper anyway (you can filter by country, too — buying from someone in your country is usually easier and cheaper).