I bought a Viking #1 in 1995. Then they came out with the #1+. She must have a #1+, there is no hoop for the #1.
If it uses cassettes, (as the #1 does),Viking no longer makes them. You may find them on ebay. The last time I needed a part for my Viking, it took forever. And when I checked with another sewing machine shop, they also said it's hard to get parts for the older Vikings.
I've heard they make the Vikings somewhere in the Far East now, so I guess they make the parts there also.
Basically my machine is a good one, but it is over 15 years old so I can't vouch for the one you found for sale.