Allister is an older, but popular brand opener. You can purchase remotes from a local door comapny. If you want a wireless keypad, you may have to install an external reciever which is in the neighborhood of $50.00-$60.00 dollars. You can also install a keypad with wires for probably around the same price. Ebay also has allister products advertised. It may be more cost effective to just replace the opener, seeings how the parts may add up to 1/2 the cost of a new opener with transmitters and a keypad included.

Thanks , it looks old , probably be better off just replacing it