Can you confirm that you've tested those pens yourself? I can't see any reference that those Gateway models use Penabled technology, so I wouldn't have thought that they would work with an IREX.
The ebay link you provided is finished, but these ones look the same and are still available:
http://www.ebay.com.au/itm/Gateway-S...item1c159a32db look just like the ones you mention/
If you can confirm they work I'll go ahead and buy one. Otherwise it's 3 times the price from Wacom.
Thanks!