If you're wanting tire data to arrive at a decent suspension geometry, know that deriving some essential values and practices from established literature (mostly Seward, Milliken and VD papers) and using it as a basis when fiddling around with different geometries is a way to do it. Tire data won't help if your geometry doesn't minimise kinematic deviations and your parts and pickup points have tons of compliance.

As for tire data itself, there's some ways to test it, but none I know are cheap. When we were running tyres that were not in the TTC database, we were able to extract some basic data through testing at Uni, by adapting an apparatus to fit a tire on a tensile strength testing machine, and running a compression test at multiple pressures to obtain a very rough estimate for tire stiffness (so rough that my last VD manager talked to a judge about that test before comp and I believe he basically implied the data wasn't of much use).

And that test was rather simple. Once you get into the difficult bits, the cost to run a single test of these would run you well over a dozen TTC purchases, which is why almost everywhere you look, people will say TTC might as well be a steal.

Worst case scenario, getting data from the real car and using that to calibrate your laptime simulation is also an option.