On a ls650 Suzuki savage and v star 1100 Yamaha we have problems getting oil from shops can you use a really good car oil in both?

no you cant use oil that would be used in a car on a motor cycle, cars have dry clutches and motor cycles have a wet clutch,, so the oil that is used in a car is lacking some of the properties oil in a motor cycle has.

Yes you can use good quality car car motor oil in your bike, I have a 1999 Yamaha VStar 1100 with 90,000+ miles on that has always been run on Castrol GTX 20W-50 and never had a single problem, have several riding buddies that use Castrol in their bike's including a couple Harley owners, none of us had ever had a single problem.