Excluding bonds, is there some kind of guaranteed return vehicle you can buy?

I started a Roth IRA. If I put money into it but have no good stock investment ideas, what can I put my money in for a safe return as I temporarily wait? I was hoping to temporarily treat it it to be like an interest-accruing savings account.

My broker apparently does NOT offer bonds like treasuries, which would be the ideal option. So I'm not sure what kind of vehicles are out there that match this description. In fact, is there anything out there like this? I know the S&P500 is usually safe long term, but it is out of the question because I believe it will fall from current levels. I'm looking for something like a bond that will return my money to me and have the option for liquidity in less than 6 months if needed.