Bodybuild

I do not have access to a machine that i can do cable crossovers on. Any advice for dumbells instead? Also, what are some good exercises for targeting the upper pecs?

The best one is parallel bars dips. With weights work for lower/outer chest.
Also - declined bench dumbbell press and flyes.

Declined bench dumbbell press and flyes are for outer and lower pecs. For upper pecs you need inclined presses and flyes.

If you have a home gym/weight machine with high or low pulley attachments you can simulate the movements of a crossover machine by exercising one arm at a time. I have also been told though I dont know if it is true, that you can also simulate crossovers with dumbells using a flye type movement but instead of stopping at mid chest pulling the arms as far over to the opposite side as possible. I'd guess that that flye type move might be best simulated one arm at a time. (if anyone knows if this is true I'd like to know)

You should not do the same movements with dumbbells , when you move further than the middle of the chest, you lose effect of dumbbell weight.
Nothing can replace cable crossovers