The formula dealer should be able to set you up with the original ladder that went on the swim platform.
If not West Marine does have a couple of all stainless steel ladders available a short one and a long one. You mount a stainless steel clip on the platform and it slides into it. You can remove it easily. There are also several different designs availble. If it was me I would try to keep the boat as stock as possible.
Enjoy!