Here's some options on grips.
As above, grips for the original Trooper are the same as Python grips.
Be aware that people often sell "Trooper" grips that are actually for the Trooper Mark III. Mark III grips will NOT fit the original Trooper or Python.
Original Colt factory Target grips typically START at $150 these days.
http://gungripsupply.com/
(These are the same grips that Colt used on the last of the Pythons in the late 1990's).
http://www.eaglegrips.com/guns/Python-Official-Police-grips.html
(More Expensive but NICE).
http://www.badgercustomgrips.com/colt_pistol_grips.php
http://www.getgrip.com/
(Hogue is sort of the "standard" for many Colt owners.
Note that they offer options like grips with or without finger grooves.
The bottom mount saddle mounting device is a little aggravating to install, but it gives the most solid mount of any grip made with NO shifting or moving).
On Ebay several South Asia makers are selling "sort of" replica Colt type Target grips. These are offered in the Second and Third type Colt Target style.
These are decent for the price, but in no way are they Colt quality.
Also note that the "Colt" medallions aren't. Look close and they're very different.
Here's some examples:
"Replica" Third Type:
"Replica" Second Type: