I have this great PDF in Russian (a lecture authored by Kashkovsky - "Forage base for beekeeping"; gotten from a free online library).
Hanging up here for a general use.
This is a list of plants native to Siberia and targeting Siberian beekeepers.
Easy enough to google-translate.
OR - copy the Latin name - paste it into the Google and read on.
OR if you spot a very good production numbers in the description (e.g. "500 кг/га" ~ 500kg/hectare - this is for Leonurus cardiaca (motherwort) - Google it up).
While most of these are native to Eurasia, they are now common place in N. America, like it or not - they are here to stay already and maybe even grow on your property.
So, if one wants a good nectar producing pasture for the Eurasian honey bees, these plants belong there.
Many of these plants are for sale in the USA anyway for various usages OR just grow in wild.
Disclaimer: these are NOT native North American plants; so - be warned and decide for yourself.