here's a link to a mod done to a WF500... which is a very similar light. Post number 8 by Plasmaman
now runs a WA1111.
not sure if anyone ever discovered whether or not a WF500 bulb would screw into a R500 reflector.. or whether the WF500 reflector would fit in an R500 head or vice versa.. BUT, if they were interchangable- WF500 bulbs are available for about $10 from qualitychinagoods.com