There are a number of such companies/agencies out there. These probably aren't travel agents per se as timeshares are real estate and fall under different rules. Most travel agents are really just booking agents for larger agencies and these booking agents can't actually hold unsold inventory of anything. They just make reservations for clients directly with the travel provider (cruise lines, resorts, hotels, etc) and then earn a commission.
There are companies out there that you can allocate your weeks or points to, and usually give them your login credentials. They then find people to rent them to and make the reservations and make guest name changes. Or if you don't provide login credentials, they then have to come to you to add guest names and such. These companies make money off the spread of what they rent your week or points for and what they pay you for it.