Do they still sell a similar, modernized weapon?
A number of different ones.
http://www.quackenbushairguns.com/
These have taken bison, black bear, and hogs. At close range it looks to have the performance of a slow .45-70.
There are a lot of pre-charged pneumatics on the market but they tend to be very expensive. I think several models are made in South Korea. I have personally never even seen one and I have a couple dozen airguns.
I do recall seeing a video of a buffalo being taken by one of the PCP guns.