I'm looking for just the 2x barlow group (threaded for attaching to a standard 1.25" EP barrel) to use with a binoviewer. The GSO 1.25" achro/shorty barlow is one that would fit the bill: the achro lens group unscrews from the barrel and onto any 1.25" threaded-for-filters EP. But any other low-power 1.25" screw-on barlow lens with half decent coatings would be fine.
The binoviewer I got came with correcting optics (1.8x and 3.0x) but the 1.8x corrector is made with only <10mm of clear aperture, which results in unacceptable vignetting with most EPs I'd like to use it with.
If no offers, I may buy a GSO 1.25" from Andrews for $39. That'll be $49 with postage to Melbourne. (Could have got it from Bintel Melbourne for that but I've just learnt they're no more.
) This should also give you an idea of how much I'm willing to pay for one.