591/594 contributor data is available via WA gov Public Disclosure Committee online querying system.
WAGR 594: http://www.pdc.wa.gov/MvcQuerySystem/CommitteeData/contributions?param=V0FTSEFHIDEwMQ====&year=2014&type=initiative
POGR 591: http://www.pdc.wa.gov/MvcQuerySystem/CommitteeData/contributions?param=UFJPVE9HIDAwNQ====&year=2014&type=initiative
Surprise, surprise - 594 reads like a long list of Seattle neighborhoods sponsoring the initiative with boatloads of money, while 591 is funded by far sparser amounts spread around the entire state.
NOTE: there are a row of buttons at the top of the table columns, one of which is a small Excel icon - you can use this to export the entire list to CSV format for viewing/sorting on your PC in Excel.
Oh and the kicker? I live in a long dirt road out in rural Pierce county. I was picking through the 594 list by ZIP code, and found that one of my neighbors on my road was a donor to WAGR. Nice guy, we have chatted a few times, he walks by my house and at the bottom of my property a lot, but frankly it annoys the shit out of me to know this. Trying to decide if I should talk to him about it the next time I see him. Either he's misinformed about what 594 does, or he's perfectly aware of it and will subsequently write me off as a "gun nut crazy" after probably saying some stuff to my face about being "brainwashed by the NRA and GOP."