How do I buy some? I have some investment funds
Treasurydirect.gov. They are indexed to the inflation rate.
The maximum you can invest is $10k/year (you actually can go up to $15k if you include your tax refund, but lets keep it simple: $10k max).
You'd need to sign up for an account at tresurydirect.gov.
You can't purchase the i-bonds through regular brokers.
You'd need to hold the bond for a minimum of 1 year. You'd need to hold it for at least 5 years without forfeiting 3 months of interest (i.e., even if you reimbursed the bond after holding it for the minimum of one year, you'd still make more money had you held it in the bank. Even with forfeiting 3 months of interest).
Setting up the account and the ability to transfer between the treasury account and your bank account can be a pain. I had to get a "medallion stamp" from the bank (one step up from a mere notary stamp).