Just been installing a Grohe (http://www.grohecatalog.com/) Rainshower
head (Part Number - 28 373) which has a 'G 1/2"' Female inlet.

I was planning to use the chrome Grohe Shower Arm / Nipple (Part
Number 28 492) which has a 1/2" NPT-MIP (Male) at the supply end...and
a G 1/2" Male at the end to connect to the shower head.

Unfortunately this Shower Arm is too long - 12"...I just need a 4 1/2" arm/nipple.

Grohe only make the one size of the shower arm. I think I've
understood the 'G 1/2' inlet on the Rainshower head means I can't just
walk into any plumbing supply store and buy a standard shorter nipple
with NPT mail threads on both ends...correct?

I need advice on how to proceed?  

-- An alternative supplier of shorter nipples with 1/2 NPT-Male threds
on one end to 1/2 G threads on the other end

-- The type of company who could cut and re-thread this existing
nipple at the NPT end.  It is solid brass plated with chrome.  One
place I went to said a) the could only cut/thead steel pipe and b) the
laith would likly damage the chrome finish...and so I would need to
find someone to replate the nipple once

I live in Toronto, Canada...so local ideas would be best

Thanks
Antony

talk to Jordan at www.paulsupply.com
(877) 232-9721 . he can help