email them (I don't know if they answer them, I never tried) or better yet, call them and ask for Bob Bell. He's been in the business for about 35 yrs. If he doesn't know, i'm sure he can point you in the right direction.
They sell Marklin and LGB, but I have no idea if they handle Bertren.
Ibertren have been out of production for some while I believe. They made N gauge locos and stock AFAIK. But your google search will come up better with the right name. HIH
Shortliner(Jack)away up here in the Highlands