I assume you are interested in having an income from 3d modeling.
In grabcad only being an engineer and winning challenges.
Are other communities or websites where you will be able to sell you work or get jobs, but you need to be good at that. gaming characters, scenes... gaming industry, architecture, movie industry, marketing...
Do a proper internet search.
You will need to be good in 3d modeling and to have a proper portfolio, or to be a good animator or a very good render.
3d modeling for gaming industry or 3d modeling and render for architecture are a common jobs and if you will have a proper portfolio and lower prices then other, maybe you will be able to find some jobs, by sending you portfolio, price list with an job or collaboration request to different companies, maybe will help you to find something.
I've not seen many 3D StudioMax users on this site. I'd say this is primarily a site frequented by CAD program users.
Certainly, I think everyone is welcomed here regardless of software. I'd look at a site geared more towards 3DS like turbosquid.com There appear to be many users/artists there who sell their models.
I suspect that selling your models will require having a decent portfolio as Ioan mentioned. Listing models on the site could also lead to requests for custom work if people like your style and presentation.
I love the staircase image in your projects, but the CAD data associated with it, does not look anything like it. Be very careful selling models. Clients will expect exactly what they are paying for (usually more).