I bought the original Model 9 MSR stove from Larry Penbarthy, they cost less than $20 when first introduced. Every year I would go to the Northwest to climb and hike and every year I would stop by MSR at SeaTac airport and take the stove in for a checkup. Every year I would get traded at no cost to the latest version. Those were the days!! Since REI took them over, things have changed. I took my pump in because it was allowing fuel into the pump and the person at the REI store took it apart and lost my ball which is a critical part of the valve. Dead pump! Thanks REI.
I heard somewhere that if you had an old yellow pump they were replacing them for free with a newer pump, but that's been awhile. I would write or call MSR tech support and see what they say. I do know some of the variations of the XGK and earlier models had some interchangability. There may be a whole pump assembly that would fit your stove or some parts kits available from MSR.
I still have 2 of the yellow pumps, one with the trashed valve and one in pristine (although probably not working) condition. Not sure I have the cup either although I did use the cup when I carried the stoves back in the day to keep the wire pot supports from poking things in my pack.
BTW, have you asked HikingJim for advice? He is the stove guru and known around the world for his excellent stove information.