Auctions for treasury bonds occur eight times each year: February, May, August and November are original issue auctions and March, June, September and December feature re-openings, which are additional amounts of previously issued securities. All treasury bonds are now issued electronically and no new paper bonds are issued.
If you would like to place a non-competitive bid on a treasury bond, you may go through Treasurydirect.gov, but if you want to place a competitive bid, you have to instead go through a bank, broker or dealer to place the bid and acquire your bond.