SPICE Model For Voltage Reference
These are complex devices containing many transistors and components, so any SPICE model will be a macro model, made up of voltage controlled currents sources, Current controlled current sources , Voltage controlled voltage sources etc. etc.  and the only people who can do that reasonably are the designers themselves.

Look on the Maxim website for these models, if they don't have them look to someone who second sources these parts and might have done it.  The company that is best at this is LT itself so I'd suggest seeing if there is a close match and then it would be likely that LT has these devices in the library for LTSpice.