do private military contractors get pensions?

That's like saying 'do doctors get pensions?'
There are dozens, maybe hundreds of companies out there as contractors for the military. There are probably a dozen on my own base providing IT support, janitorial services, running base supply, providing additional personnel to who knows how many different offices, etc, etc.
Every company has it's own 401(k)s and pension plans. Like any private company, you probably won't see a dime until your 50s or 60s.
Now, if you want to get into all the companies providing services in the desert and other foreign locations, a lot of their employees are TCNs (third country nationals--people from places like Africa, Latin America, and SE Asia) and locals. These people get paid a couple hundred bucks a month, plus a bed and three meals a day. My bet is that they aren't getting a pension.

Not from the military

you do ot know as much as you think you do

do you even know what a PMC is ?

99% of PMC's do not even carry weapons, they do things like cook, work in ware houses, do laundry, etc

2. and like any civilian job, a pension is based on if you work for a company long enough to retire

3. most PMC's make less the 60k a year

I don't believe Academi (formerly Blackwater) offers company defined/supported pension plans....but they do pay well for Elite front line unit combat experience...I had two buds in my battalion that signed with BW after their enlistments ended in 2005...they both signed contracts in the $125K/yr area.

Not from the government.

Depends on the perks offered by the Company that they work for.... What part of Private Contractor do you not understand?

Depends on their company benefits

As in a pension from the government like my military pension. No they don't but some companies like Bowing, McDonnell Douglas and what not offered pensions in the past. Today though few companies offer pensions and instead offer 401Ks and other employee funded retirement plans. Something like less than 3% of the companies out there still offer a pension or employer funded retirement plan now.

Some do offer bonuses and other financial type rewards though and I have several friends that are military contractors who make a decent buck. I myself have done some contract work for a couple of companies in the past and the pay was decent enough for what I was doing but that was nothing long term like what many of my friends do on an ongoing basis.