I'm unsure of what source would be appropriate here. I can't point you to a lack of a thing, by definition.
1. You can point to a source with some authority talking about the lack of a thing. Which shouldn't be too hard, since, unless you're ex-Russian Army logistics, you must have learned those claims from somewhere.
2. You can point to a source talking talking about Russian Army logistics, that shows them "moving things by hand" when forklifts would be more appropriate.
3. You can point to a source talking about how all forklifts require really flat concrete, and not all countries can make it because [reasons]. However, you probably can't do that because that would contradict the example I gave of a forklift operating on gravel.
Most of my evidence here is fueled by what I've been seeing and hearing via the internet, so take it with a grain of salt. I'm, thankfully, not in theater. That said, these sources do seem to be 'experts' of some sort or another behind their own fog of war:
War on the Rocks, podcast and online
Foreign Policy Magazine, online edition
Washington Post, print and online
New York Times, print and online
Philips P O'Brien, publications and twitter
Trent Telenko, interviews and podcasts and twitter
ChrisO_wiki, twitter
Go ahead and look in the older work if you're curious to find more out about the logistical mountain that RF is facing. The concrete thing, though a bit curious, does seem to bear out in photos of their ammo dumps and RF's inability to cure a pad before rebar is stolen (WaPo, NYT, and ChrisO_wiki are good on this issue). Gravel isn't going to work for such repeated use in wet conditions. To move those loads you'd need very large tires to distribute the weight, something like a JCB. Something that RF also seems to be without. Like, they really do seem to be that corrupt and incompetent.
> The concrete thing, though a bit curious, does seem to bear out in photos of their ammo dumps and RF's inability to cure a pad before rebar is stolen (WaPo, NYT, and ChrisO_wiki are good on this issue).
However, the reasoning you give here makes the claim more credible, since it makes clear the problem is corruption not technology.