ROPS for YM155D ?

[Lopez]

Bought my 155D thru eBay from the state of Oregon. Had 460 hrs on it and runs like new. But it doesn't have ROPS and most of our place is hills. Was ROPS available from the factory, on the 155D? Anyone know of a source?
Which tractor of the 20-25hp class has the lowest CG-something like the Kubota BX series?
Thanks,
Don