oil shop @ Ankara, Turkey? or Istanbul..
 

Our bikes really need an oilchange (which I will do myself), we we need a few liters of engine oil.

Any tips (and GPS-coordinates?) of a good shop in Ankara, or Istanbul?

We hope to find some Castrol semi-synthetic or something. No automitive-oil from the gasstation...

You can find some motorcycle oils in Bauhause, Koctas and similiar places. Also, you can find them in some gas stations but you need to ask "Dort zamanli - (4 cycle), Motosiklet yagi (motorcycle oil)". If your bikes are 2 cycle, ask "Iki zamanli motorsiklet yagi".

Or...

If you see someone who rides a good motorbike, just stop him/her and try to explain you need an oil change.

Be sure it will work and he/she will help...

Kobold's advice should work well too... i make my recommendation in case of if any fuel station is not visible nearby...