Sprinta: Most engineering paces should be able to do the reaming for you... Im not sure where you can buy the actual tool from.
DJ345: I bought my lower control arms from EKW, there a bit expensive but can get a lot of parts too...
Simon-MrRx7: Do you know what model Sigma your arms are from? I measured some on a sigma (not sure what model) at my mechanics and the arms were only 300mm long, the same as RA60... I.E. Not much good with RA60 struts.