Garmin Nuvi 500 topo map update?

[Blind_Io]

The maps on my Garmin Nuvi 500 are long out of date and I'd like to update it. The problem is that the only updates I can find from Garmin are only street maps - no topography. I'd very much like to keep my topo maps, as that was a major factor in buying this GPS in the first place.

Does anyone know of a place I can get topo/highway maps that are compatible with the Nuvi 500? I'd also be interested in maps of Baja, since I'm headed there later this year.