according to motodepot.com the progressive springs (progressive pn.11-1128) will cross to the following bikes. allthough the gs requires a spacer length of 0.75" as far as I know the stock spacers can be cut to this length so all you will need are the springs. I crossed a few of the listings into the progressivesuspention.com database and they all came out with the same 11-1128 part number. allthough they had different spacer lengths. on a side note the springs were listed on motodepot.com for $59.95 + shipping.
HONDA
VT500 ASCOT (TWIN) 83-84
VT500 SHADOW (TWIN) 83-84
KRAP-A-SOCKIE
VN750 VULCAN 85-02
EX500 94-96
GPZ500S 94-96
250 NINJA 88-97
YAHAMA
1100 VIRAGO 86-99
1000 VIRAGO 84-85
750 VIRAGO 88-97
700 VIRAGO 84-87
XJ700X MAXIM 85-86
FJ600 84-85
FZ600 86-88
SRX600 86
YX600 RADIAN 86-90
RZ500 85
AFAIK, the springs still sell for $57.95 at Motorcycle Accessory Warehouse (MAW). See the first post in the Chaparral price hike on Progressive springs!!! (http://www.gstwins.com/forum/viewtopic.php?t=10732) thread for links.
Be sure to compare the shipping rates, just in case the cheaper item is actually more expensive as a result.
from what I thought a yamaha radian was the same bike as a seca2 right? well anyway, the seca2 uses a different spring than the gs acording to the chart. but the radian uses the same spring as the gs. someone had metioned that they had gotten radian springs for like 15 bucks on a ebay closeout so I was thinking about it today, and you all see the result.....
found these on ebay, shipping is going to be between 10-15$ way over priced as far as I am concerned.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&tc=photo&item=2488972998&category=35592