well
There is a long and short answer for your question. and basicly both of them agree bottom line to no you can't. but there are some variables.
some distrubitors offer alternate grips. (I think Texas Jack did, but usually they end up to be from Buffalo Bros or others.)
Some distrubitors will change out the grips after they hit stateside. (EMF does this sometimes, esp. when they do a custom finish like the fancy nickel plate or have the Turnbull cch done..so..
Often times the distribtors will have spare grips in stock or laying around as spare parts.
But here is where the long answer becomes the short answer:
If you look inside your factory grips, you should find a number marked, usually a 4 digit. Those digits match up to the serial no on your gun. Grips are fitted when they do the final fitting at the factory (that is why your backstrap mates so well to your frame.) Then when the gun is finished they can put the right grip on it. So, you won't see them change out grips very often because fitting grips is time intensive, and time is money and that will reduce what little they get in the first place. So, the amount of spare parts grips are slim.
Best bet is to find a grip you like and get it after market and fit it yourself or have it done. I have fit several of my own and I have also paid to have some fitted. My gunny charged me $50 a pair to fit my ivory grips. Out of all my guns (including nonCAS, I think I only have 4 guns that have original grips on them. 1 even has different tg/bs and grips.)
So, best bet is to contact the distributors and ask if they have any spare grips (ie EMF, Cimmiron etc) but usually they will only have stock stocks...heheh like wood one piece grips) but don't hurt in askin.
good luck
curley
PS: did some checking around and I was right Cimmaron has grips listed in the Custom shop..they have TruIvory and Sanbar Stag, but appears they are for fitting to a gun you buy from them, and under grips they list SAA hard rubber and Lightning hard rubber for about $60 a pair and of cof course "require fitting" their number is (830) 997-9090 When I got my all blue Great Western, I bought a set of Colt Hard Rubber for it and my gunny charged me $50 for grips and fitting.

Great Western with rubber grips and Colt
Check my web site under Just for fun gallery and see my guns and their custom grips
http://sdough.smugmug.com