Dumb question number 1 - what oil for my CB750?

[centerall49]

I have a 1981 CB750K and I need a little guidance on oil.  Nearest Honda dealer is 40 miles away.  We have a Yamaha dealer in town.  Can I just buy oil like they would use in one of their in-line four models?

My manual says 10w-40 or 20w-50 and I live in Texas with temps around 100 this time of year.  So shouldn't I go with the 20w-50?

Would there be motorcycle oil available somewhere else besides a motorcycle dealership?

Finally, where do I get a filter?  Do I need to drive that 40 miles or is there an easy mail order answer on the internet?

Thanks (I know cars better than motorcycles)

[Re-run]

Just us a standard 20-50 oil. It does NOT need to be a bike oil.