You have to solve two problems -- your place of citizenship and your place of residence. Dominica and St. Kitts are the two places most people look to buy citizenship. There are other more expensive places too.

Residence - this is easier to arrange. If the country will give you a tourist visa you're in, at least temporarily.

I believe that's Singapore. Albeit, the rules are being changed due to rapid influx of rich foreigners into Singapore causing social issues. https://sg.news.yahoo.com/ferrari-crash-fuels-singapore-anti...

If you have lots of money, you can buy citizenship and a sweet tax deal from one of Switzerland's municipalities/cantons.

Two separate issues there :)