Just in case you are still looking for other soundbites, maybe these can help (emphasis on maybe). None of these feature a simple, classic carnival barker routine, and I haven't come across any that just have a single voice track without background noise. Still, in case you or some one else may find something with potential, here are a few sources that have a barker doing his thing:
The first listing on this page has a barker doing a rather classic spiel. Unfortunately, there is a lot of background walla, and I'm not sure if you would be able to isolate just the barker's voice by using a program like audacity.
Vocals - Carnival Barker - Medium - Carnival Barker with Crowd Walla (MONO) Festivals*Crowds*Sound Effects*Downloads
This is a brief barker spiel at the start of Creature Feature's "Greatest Show Unearthed" track off of an album of the same name. The problem is that it is part of a song and the background builds up to that, and I'm not sure you want the background noise or all the hints that a song is about to start. You can listen to it here: YouTube - Creature Feature- The Greatest Show Unearthed~ With Lyrics
Another is called "Dark Carnival" off of Introsound's (aka Dr. Goodsound's) Twisted Circus: Creep Show CD. I recall seeing this CD in stores for at least a couple years and it is readily available through download. This track features a very cheesy barker saying: "welcome to Twisted Circus Two, the darkest carnival on earth. Where things are never what they seem to be...they're much, much, much, much worse. Because at Twisted Circus Two, the spirits of evil will try to tempt you with their voice. But watch out; the price of a ticket is your soul, and there are no refunds! So, as you party along and enjoy the night, just remember one thing: this night, could also be your last! [demonic laughter]". Aside from saying "Twisted Circus Two," the fellow doing the voice acting isn't ...great...at doing an eastern European accent (but at least it sounds like he's having fun). I'm not sure if this would be that much better than you or a friend reading some lines in a deepened voice. You can hear a clip here: Amazon.com: Dr. Goodsound's Halloween: Creep Show: Various Artists: Music.