I think that technically it may not be legal to sell a product containing oleander in the United States since it was put forward as the basis for an investigational new drug (IND) by Ozelle Pharmaceuticals. However, companies do not seem to be having a problem getting it shipped through customs, so perhaps there is a loophole or just lax screening of goods.
There is a product based on the remedy called OPC (it contains 80% oleander extract prepared exactly according to the remedy and 20% supportive botanicals) which sells on the internet at a couple of sites I have seen for prices ranging from $299 to $345 per 500ml bottle, but I am a bit concerned about the reliability of those sites.
The best source would be the patent holder for OPC in South Africa, who combines the oleander with 20% South Africa Cancer Bush. Until recently, he had sold only by word of mouth and referral, but due to popular demand, and some problems with the other sites he had licensed the product to, he now has his own site up:
And he only charges $99 including shipping. I am not trying to push his product here - after all, you can make it yourself for pennies. But I do know the patent holder from my research and can vouch for him most highly.