Ukrainian philately has its own specialised societies, not only in Ukraine but also in the USA (UPNS) and in France (SFUP). I guess the UPV still exists in Germany, where it was once the world's most important vehicle for research in Ukrainian philately.
Despite these organisations, Ukrainian stamps and postal history 1917 - 23 seem neglected. Partly, this is because there is actually a lot of material available. For example, for the year 1919 when Russian material is very hard to find (and most of it without stamps), Ukrainian material - and with stamps - is quite plentiful.
True, for some parts of Ukraine material is scarce (Poltava, for example) and true, mail going abroad to anywhere except Germany is hard to find.
But against this, common stamps are common and Money Transfer Forms are actually not scarce. The basic catalog listing in Michel - based entirely on Dr Seichter's work - is excellent. The illustrations are all accurate and reliable. Compare Yvert, which is dreadful!
But there are whole areas which are under-researched. Tariffs, for example - though we now have the work of Alexander Epstein; the use of Ukrainian stamps by the Bolsheviks after the Sovietisation of Ukraine; and even the dating of Trident introduction in 1918: if I came across a First Day of Use cover in a dealer's box, I would not know that that is what it was. [ But as free advice: if you see a genuine Trident cover with an August 1918 cancellation, buy it ]
In September 2011, Corinphila in Zurich will auction the Ukraine collection of the late Dr Ron Zelonka. It is much more than a Trident collection (it covers the whole period 1800 - 2000). It will be the first time that a specialised Ukraine collection has ben offered, broken down into Lots, since the 1987 sales of Vyrovyj's collection by the Swiss auction house Schaetzle. It will be a very interesting sale!
POSTSCRIPT 17 January. I was just looking at the latest Michel catalog for Eastern Europe (Osteuropa). They have scrapped the very good Ukraine listing which took up only a few pages and replaced it with something that looks useless! Nicht intelligent! All the more reason to use John Bulat's catalog: go to upns.org to order a copy