The OP needs a RCK60-22BX. This directly fits the BX2200. As far as I'm aware, there is no other substitution for this.
As what others state, the correct deck is the "metal everything", except for the gauge wheels which are hard plastic.
Also, if you get one used, I highly suggest looking at it in person. If not maintained (greased and gearbox oil changed regularly), you can be stuck replacing bearings and potentially an expensive gearbox. Most people get rid of theirs because it's cheaper (and easier) to buy a used rear mount finish mower than try to fix it. So buyer-be-wary.
Edit:
I just looked on the interwebs and I see 3 of them out in MD. Judging by the pictures of all 3 of them, they seem questionable. But $1,200 a pop, if all is good on them, all you need are gauge wheels. All 3 of them look worn out. So the decks are available, but again, I highly suggest looking at them in person, and if possible, bring someone out with you that has some automotive/tractor repair experience before plopping down cash.