I’ve written about several cases where Americans have adopted the British tendency to pluralize attributive nouns: to use drugs party, covers band, drinks menu, and books editor instead of the customary/traditional “drug party,” “cover band,” “drink menu,” and “book editor.” Check out those links if you’re interested in the ins and outs of the issue.
The latest instance comes via a current National Public Radio (NPR) corporate underwriting spot, intoned by the same plummy-sounding woman who (in another spot) talks about “what-if scenahhrios.” In this one, for Amazon Business, she touts the way it “helps simplify the supplies-buying process with a one-stop shopping experience.” The typical American term, I submit, would be “supply-buying process.”
I acknowledge that I can’t prove that. Both variations of the phrase are uncommon enough that Ngram Viewer and other tools aren’t able to shed much light. However, I can report that “supply buying” has been used nine times in the history of the New York Times and “supplies buying,” as of now, has never appeared in the paper.
If anyone thinks I’m off-base here, please have at me. (Not that you required encouragement.)
notoneoffbritishisms.com 
This is a case where both supply-buying and supplies-buying seem normal to me as American usage. In fact, supplies might even fit better if you turn the idea around and think of someone saying, for example, “I’ve got to run out and buy some supplies.” I think of “supply” as a verb or a particular quantity (we have a good supply of chewing gum), but of “supplies” as the category.
Is she a plummy sounding American, or a plummy sounding Brit? Does a plummy-sounding American sound like Eleanor Roosevelt?
American–and yes, a bit like Eleanor!
I must admit I was surprised by your characterisation of this as a “British tendency”. Im 100%, full-fat Brit and I don’t recall ever hearing or seeing “covers band” or “books editor”. However, nor have I encountered “drink menu”, which sounds very odd to my ear. So perhaps there is no consistent rule in BrE here.
I am aware that BrE follows collective nouns with either singular or plural verbs, depending on context, whereas AmE almost exclusively uses singular verbs. However, the examples given do not fall into this category. Party and band can be used as collective nouns, but not menu, editor or process. The words preceding them are all being used adjectivally.
Phoebus, I was incorrect in calling “drugs,” “books,” “supplies,” etc. “collective nouns.” The correct term is “attributive noun,” and I’ve changed the post accordingly. More on plural attributive nouns at https://notoneoffbritishisms.com/2015/06/10/covers-band/
I think corporate lingo in the US would favor “procurement” over “buying” in that context, but either “supply procurement process” or “supplies procurement process” would be unremarkable.
It strikes me that we have “sports bars” in the USA, where presumably the British equivalent would be a “sport bar.” “Sport/sports” is a particular case, however.
It would appear from Google that we call them sports bars in the UK, probably because it’s an American concept. Normally in the UK you don’t go to a bar, you go down the pub (which will have bars in it).
In the same way that we read about sport in the sports pages, watch sport on sports tv and study sport at a sports college.
I hope you have the data for this proposition!
Perhaps we could ask former Directors General Dyke and Thompson for help with this?
I’m a Brit, and I do not say drugs party, covers band, or books editor, but rather drug party (were I to use the term at all), cover bank and book editor. However I *do* say drinks menu. Weird.
As a British author, I would regard a book editor as the person who tries to muck around with my perfect prose, while the books editor is a more senior figure who decides which books to take on and perhaps decide how much editing the book editor will need to undertake.
On both sides of the Atlantic newspapers have a “books editor”, the person in overall charge of the Books section who commissions individual reviewers (and edits their copy, no doubt).
Glad you wrote this post. I hear the ad often, and “supplies-buying” sounds like nails on a chalkboard to my American ears.