why cant i find outdoor ho scale track,its not ok to run out side and why

i have a gp40 diesel loco that came dcc on board from bachman as a set with the EZ command controller i am wishing to add sound to it is there a decoder that i may use or some one to talk about opptions for upgrading to sound 

i have a gp40 diesel that came with the ez command controller. the controller broke ?? replaced it with prodigy express

adding sound to already dcc equipped bachman trains. which decoders should i use