Any advice on where I can look at investing in Treasury on the open market?

So I think bonds and Treasuries are going to be investable in the next 12-18 months. I am not going to do corporate bonds as that would require understanding the company, cash flow, and its position in the industry and macroeconomics. I prefer simply US Treasuries, in the 2, 5 or 10 year duration.

I know you can buy from TreasuryDirect, but you can't sell them unless you transfer them to your brokerage, and that's an extra step that could have issues (i.e. I've had issues transferring funds before between brokerages.)

Am I able to buy the Treasury notes on the open market at my brokerage?