Tomix HO scale panto's would be your first bet. Might be able to get them via ebay or a tomix retailer.

Apart from that you can contact micro models in Hornsby as they are on the verge of releasing their 85 class kit complete which might be a better option.....I've seen it and its very very nice.
They may be able to sell you the pantograph s separately anyway.

Regarding the mechanism, I would think very carefully before committing to such a project as I tried many years ago with a austrains 80 class as the basis and it was just too messy. The 80 class would be a close match but the wheel sizes are wrong and I doubt the friedmont body would fit too well.....