At my last shop, we had similar problems. We got around it by including extra equipment we wanted in our server orders. Accounting never bothered asking why we needed nice keyboards and big monitors for rackmount servers. But god forbid you try to buy those directly. At one point management started to get wise, so we just had the vendor include the extra equipment in the same line item as the servers instead of broken out, just increasing the per-server cost to account for it.

Shenanigans like that shouldn't be necessary just to get the stuff you need, but big corporations are so dysfunctional sometimes.