Why not build one from scratch??
Here's a brass HO column...with lots of good pics...for reference...
Oil Column Link
Tichy makes one in HO (#8169) of an alternative style (Sheffield)...very common in the era. The Tichy one is quite inexpensive if you wanted to have something for reference in upsizing to O.....
Tichy HO Oil Column Link
...for which plastic/brass/aluminum tubing would be a good starting point. Plastruct makes some plastic pipe (valve) parts. Brackets, wheels, funnel...all fairly simple to scratch/buy.
The pedestal base shown in the brass photo? Check the model ship parts suppliers. That sort of tapered base is very similar to stylized mounting pedestals they offer in different sizes. We (LHS) have a few in our wooden ship models section.
Anyhow, the Tichy HO would give you good reference for dimensions (x2, of course!).
Notice that the HO model in the link sold for $100. Well, good grief Charlie Brown!!....I can't imagine even paying that much for the O scale brass version!!! For the cost of materials and a few key parts, I'm thinking in the $10-15 range....MAX....for a scratched model.
BTW, K&S makes a nice tube bender....device for minimizing the collapse of tube walls when bent. Not at all expensive....handy to add to the tool box. This would be useful if you wanted to replicate in O the column in the photo of the brass model.
What's nice about the alternative style, as in the Tichy kit?....all pipes are straight, no bends.
Just a suggestion......FWIW, always.
KD
Hmmmm...... I'm feeling challenged. Think I'll try doing the Tichy-style column!
P.S...If you go to trade shows or larger train hobby shows....and the Tichy folks are there!!....put a bug in their ear to make O scale versions of their VERY nice HO kits for both water columns and the oil column. Last time I talked with them, they measure demand very seriously. EXCELLENT, inexpensive parts & kits.