The original sculpt of the Thor (AR20-602) has a three-pack of missiles riding side-saddle on its hips. Order these missiles (best bet is to write in and explain what part it is you need, usually they can help you with that even if the part isn't available separately on their site). Stacking two of them together should make for a perfect-scaled SRM rack. Alternatively you could use one of the ones from the resculpted Loki Prime, but it's a bit big for the Shadow Cat's body.
As for the lasers, using a second of the Gauss arms is a solid solution, but if you want something different I would give some thought to the arms from the Wolf & Blake version of the Malak, actually- it might sound a little weird, but looking at the two on my shelf, I think it might look kind of cool.
