T-Slot Companies provide different line ups, they have their own catalogues. T-Slots by Bonnie Aluminum has aluminum extrusions available in different colors. You can choose between fractional size or metric size depending upon your choice.
Companies such as Parco and 8020 provide exclusive products. But the rest of the T-slot parts are interchangeable and universally compatible. But well known companies provide high quality parts which are more reliable.
Some companies limit their products, as they don’t have facilities to provide aluminum extrusions of all sizes, do check with the companies site to make sure they have the right profile and right sizes before you order.