I noticed the previous owner had attempted to repair this before but how do i fix this?
can i buy a replacement part or do i have to fabricate something up?

 

search for a replacement shock tower. shouldnt be too expensive, and should already have all of the spot weld holes drilled into it. if not you just need to drill them yourself...all in all, you just need to get a spot weld cutter to drill out the existing spot welds on the bad panel. unfortunately, it looks like the rot also got into your fender well, so for that you might want to fabricate about a 1" or so strip and seam weld it in there so the shock tower has something to be plug welded to

 

i will probably need to buy the other rusted out panel too and just replace them both

 

First I recommend taking a wire wheel cup on an angle grinder to anything that looks like it is rusty there. Some/all of that might not be too bad/ por15 able. Some types of paints make the rust look worse than it really is.

Cover up everything well including yourself before starting, respirator, face shield, gloves, disposable suit, that paint and body epoxy is not good stuff to breath in.