There are no bolt in/swap out coilover kits for the front for your SA63 as such. Later model cars that use a strut that is seperate from the front or rear hubs get it lucky as they can have swap out coilover suspensions made and available off the shelf, as you may have found.
There are several weld on kits available from K-Mac, Fulcrum etc. They consist of two threaded sleeves which are slid onto the strut tubes after the OEM spring platforms are taken off and then they are welded in place. The kits should also provide two spring seats/collars, two more lock nuts/collars, and two spring tops and the same company can supply a suitable spring.
These are very common conversions and are done to any model Celica, Corolla, Corona etc that use a combined strut/hub assembly so I am sure an SA63 has been done before and any competent machine shop welder can do it.
You will need to measure the strut tube diameter to get the correct sleeve supplied. The SA63 strut should be 2 inch in diameter. If you measure it in metric you could end up with the wrong size. There are 50mm kits and there are 52mm kits and there are 2 inch kits.