I haven't been able to find information, prices etc to book accommodation in North America with contiki for before and after a tour. Is this available? or could it be added to the website?

It should be available - I stayed in both Contiki hotels (LA and NY) before and after my trip.

Ask your travel agent to book the pre/post accommodation for you once you know which hotel you are staying in are or, if you are booking your trip yourself, call contiki to organise it.

There is this link which gives you an idea of where you might stay: http://contiki.com.au/contikipedia/articles/where-you-stay-north-america