You could probably make Deere's 100 series 48" bagger work, bg20777. However this particular design was not set up to utilize the powerflow system so it is just a cut and throw design. I have never been impressed with the bagging capabilities for anyone's cut and throw collections system for this large of a deck. If we where not talking about baggers I would say that they suck
The big box stores usually keep the JD 100 series baggers in stock. I would buy one of these and make it fit. Just a guess but $250 to $300 for one of these. I had one that worked okay as long as you did not over load it with wet grass. Not near as good as the MC 519 cart and power flow blower but a lot less money.
Can you post a picture of the back side of the tractor behind the seat and chute side of the deck. I might have what you are looking for. I have a bagger for my old L120 that might work. Just got to figure out a way to get the bagger from the far northwest corner of the state to the far southeast corner. Edit. I am afraid that the lawn tractor you have might be the Murray manufacture model as I was looking on the web and these models are not compatible with the John Deere styles, the Murray models made with solid plastic catcher bags and the Deere models are soft fabric