IBM RAD is paid product, so unlikely someone will provide you a "dirrect link".
IBM RAD 7.5 includes full functioning WAS Base edition (7.0), you can install fix pack to WAS independently from RAD fix pack levels.
Also, you can use RAD 8, which also supports WAS 7 as test environment.
Normally when IBM releases products - they always version XXX.0.0.0, and if you need like XXX.0.0.13, you should first install product, then install required fix pack. There is no install for XX.0.0.13 version out of box.
So, the plan for you is:
1) Get RAD 7.5 or RAD 8.0 - as I said these are paid products. When you install, select WAS 7.0 as a test environment.
2) (optionally) - install latest fixpack to RAD - they are free, can be downloaded from IBM web site
3) Install WAS 188.8.131.52 fix pack (note, currently latest is 184.108.40.206) - the WAS 7 is located under RAD install folder in the SDP/runtimes/base_v7 directory