Blood thinners reduce blood viscosity increasing flow.
Aspirin is commonly used together with ephedrine and caffeine to form an ECA stack.
https://en.m.wikipedia.org/wiki/ECA_stack
Sure you can. It's called "Bronkaid" and any ol' drug store sells it here in the US. Usually you need to show ID and sign a waiver (you can only buy so much of it per month, since it's an ingredient for making meth IIRC), but other than that it's OTC, no questions asked.
If popping pills ain't your thing you could also grow ephedra yourself and brew your own "Mormon tea".