One way to come "on" quickly is to inject apomorphine. It is "usually effective within 10 minutes" [1].

As it happens, apomorphine is not something that I'd want to take: partly I'm put off by the injection; and partly by the feeling that I'd be more tied to the drugs; as it is, I can still function well enough to walk home if I forget my meds. But, everyone's circumstances are different, so apomorphine is probably appropriate for some people.

I find that going for a walk relieves many of the symptoms. Stress makes them worse.

Reference

[1] WebMD
http://www.webmd.com/parkinsons-dise...insons-disease

John