I am looking for the aluminum profile parts specs for this prusa i3 printer?
They are 2020 (20mm x 20mm) T-slot extrusions. They should not be confused with V-slot extrusions, which are similar to T-slot, but have a 45-degree slot profile to accommodate V-slot wheels.

If you are contemplating a new build, I would recommend using V-slot. Note that T-slot and V-slot come in a number of sizes (in multiples of 20mm). A 2040 profile is 20mm x 40mm, and will have two slots on the wider sides. Other sizes are available, such as 2060, 2080, 4040, and even C-shaped profiles.

You may want to use 2040 profiles for greater rigidity, especially if you are contemplating a large build volume.

Note that there are imperial as well as metric T-slot profiles. RepRap uses metric profiles.

ReRap Wiki: T-slot

OpenBuilds: V-slot