Hi Nils,
LM3478 and LM3488 have simulations enabled in WEBENCH. Have you tried creating your design and simulating using the WEBENCH panel in the respective product folders?
If you are looking for a standalone Spice model, we have that available for LM3481 which is similar to LM3488. You can download it from here: http://www.ti.com/product/LM3481/toolssoftware
Thanks,