not sure about las vegas but u can try these guys

Here is a link that might be useful: railroad tie company

Thanks for the lead, califman! Have sent them an e-mail and hopefully will hear back.

Railroad ties do not make a suitable use for a raised garden due to the creasote on the ties. Assume you are speaking of a veggie garden. The ties will rot in time. A much better alternative would be stones or blocks.

Actually I would be planting a variety of flowers and bushes -- nothing edible. Would the creasote kill the plants? Will the ties last a shorter amount of time here in the desert because of the dryness or heat? If they lasted 5 years that would be enough for now.

Creosote is not especially damaging to plants in this context. It is not a systemic herbicide and tiny quantities leaching from the ties will not be damaging. Liquid creosote will burn foliage on contact.

You should avoid prolonged and repeated contact with human skin, so think about whether people would be sitting on the ties.