I got mine on Craigslist like 8 years ago from someone that had it new. Check locally at just bike shops. If you are looking for a Bianchi Super Pista, eBay has frames up too. That Celest green is more expensive oddly. Here is a white one on eBay for $600 (retail is like $700-800) free shipping:
https://www.ebay.com/itm/Bianchi-Su...011278?hash=item59184122ce:g:Ws4AAOSwXMxcCDLe
But are a ton of frames and brands to look into. It's kind of overwhelming to be honest cause there are comments parts to figure out, saddles, brakes, etc. I would recommend a road bike cause for the gears but fixies are the cooler and cheaper option. I went the local bike route cause I needed to sit on the bike and take it for a test ride. Buying online seemed so iffy cause I just wasn't sure what size I was. Also when you buy locally, you get a year of free tune ups which online shops don't provide.
And if you really don't care, those State Bikes and City Ground bikes could be options and won't break the bank.