Believe it or not, lots of Opel and Vauxhall Omegas are sporting Catera grilles. They do it for the same reason we do. To stand out from the herd. For a '99 you'll want May 1994 - September 1999. October 99 starts the 2000 model year. They also use the term pre facelift to describe the 94-99 Omegas. The 2000-2001 are called facelifts. There's a mini-facelift too but I haven't figured that one out yet.
I almost ordered from this eBay vendor that sells the same grilles for USD$69.41 plus
$73.50 shipping cost to Buffalo. What a ripoff. I almost choked. Your guy sells it for USD$73 plus $19.50. Much better deal. Wish I had found it. Still, I would ask about additional taxes or import fees.
http://cgi.ebay.com/Sportgrill-OPEL-...QQcmdZViewItem
I ended up ordering a Kamei Sport Grille for my 2000 from a vendor in California. It's a coated steel mesh versus a plastic grille. Price, $190 plus $13 shipping. I'm paying over twice what you will so this had better be the grille of grilles.
http://tuningzubehor.com/cfb.asp?pg=...=0&veh=0&cso=0
It's been a month now so I can't vouch for them yet. They don't list the Catera but if you search for Opel Omega a bunch of stuff pops up. Since the parts are for the Omega B, and probably come from Europe, it may account for the delay.
Elvin