Rc nailed it.
If you want an authentic design, highly collectable, mechanically sound rifle, a pre-64' Winchester lever action is for you. They come in every shape, size, and caliber imaginable. However, one in good condition will cost you. An alternative is an Uberti Replica, or a newer Marlin, etc.
As far as a scope goes:
Authentic lever actions weren't really designed to put scopes on, as they eject from the top. The idea of "cowboy shooting" involves the straight up iron sights, and that is lost with the mounting of a scope. Scopes are great for newer guns, but would be hard to get on an authentic Winchester.
Calibers:
"Cowboy action" calibers are older cartridges that have been around for a long time. They are typically weaker loads, that have a slower FPS and a heavy bullet. You will see many lever actions in pistol calibers like .22, 25-20, 32-20 .38/357, 44-40, 45, etc.
Some rifle calibers are the .30-30, 45-70, 50-70, .38-55, and even some more modern rounds like a 308, it depends on the rifle and maker.
The .30-30 or 30WCF is a great deer cartridge and has probably taken as much deer as a 30'06. 45-70 is a slow, big bore cartridge used for bigger game like Elk or Moose.
You could learn more by doing some more research. Here is a good place to start:
http://en.wikipedia.org/wiki/Lever-action#Calibers
An 8-round capacity will be nearly impossibe in a rifle caliber like .30-30, by your criteria you may be limited to pistol chamberings.
Lever actions are great, but the guns themselves can cost big bucks, and the ammo is very expensive unless you reload, because not all the older guns can take the higher-pressure loads of today.
Theres millions of Lever designs out there, you have to pick which one suits your needs and wants.
Here is my Model 1873 Winchester, Mfg in 1884 in .44-40 caliber.
This is one of the "classic" lever guns and can often be seen in western movies.