Most of the people who are on the Ideal Protein products buy them from their local clinic, at the same time as they have their regular weekly weigh-ins. In the USA, the sign up process generally involves a medical examination and a form of 'clearance'. In Canada, we don't have to do that - just a discussion with our 'coach' of any medical issues, etc. a weight-in, measuring, etc., and sign-up. then generally regular weekly check-ins with their coach for general support, questions, weigh-in, etc.
It is possible to circumvent the above and buy IP products online through a website. If you decide you want to switch to IP for the duration of your trip, this could be an option in order to order some IP supplies. You could buy it online, and have it delivered to your destination in the USA. If you've visiting relatives, friends, or even staying at a hotel this could work. Just a thought. Anyway - here's the website.
This is the 'real' IP products. Many of the dieters here follow the IP 'protocol' but (generally for reasons of expense) use a variety of alternate products. You can find lots of information about the alternative products many have used with equal success at a thread here that says something about 'Alternates'. Sorry - forget the exact wording. I know two of the favorite alternate products used are Pure Protein bars and EAS AdvantEDGE RTD shakes (both seem to be quite readily available at various major stores - places like Costco, Walmart, etc. throughout the USA). Here's the thread were a lot of 'alternate IP dieters' are talking about the various products they have found that 'fit' the protocol.
Alternative Discussions Here
Many IP posters here have travelled though, and taken their IP products with them successfully - so this may well be your best option, so you don't have to change your program 'in mid stream'. The thread included in the post above mine gives lots of useful information for those travelling with IP products.
I hope you have an enjoyable trip.