i assume you mean military hardware and such
1. you don't need to. make your own, with your economy and your taxes and whatnot.
2. if you do want to buy others' stuff, either visit storefront threads, put up a post saying that you want [whatever], or if you stumble upon some nation using something you like, ask them if it's for sale.
3. please don't buy stuff and never use it. it's a waste of time, it doesn't tend to get any sort of diplomacy started with the seller (you'd think it does), and...well, it's just pointless and takes up forum space.
that said, most RP-active nations (myself included) will sell you something. some have better (or more interesting) hardware than others. good ones will have original equipment, not the same-old abrams' and M16's and AK's and old soviet rust-on-wheels.
carlemnaria barters generously
though we neither manufacture, possess nor desire to possess
we do have effective tecnologies to counter it though, some quite
unorthodox, including such exotic items as lananaran shield generators, 'laser' excavating tools (for the mineral extraction
and underground construction industries
primarily but of course arn't that selective about what they make holes
in) and verious exotic tec stunn (temporary unconscousness) devices
from what appear to be innocent decorative bracelets to vehicular mounted large scale versions that
can be effective in deep space aganst large otherwise well shielded vessles)
but as i say, we are not a warfaring nation and have no intention of becoming arms merchants
only the ability to withstand any attempt at armed takeover
(not that we have much in the way of central targets to take over for that matter,
just an extremely low tollerance for colateral dammage as a culture and a way of life)
(we love tecnology and use it to live closer to nature
and hate guns, knives, automobiles and belligerant attitudes,
yes we're tiedied, bell bottom, love bead wearing, tree hugging, peace loving
anarchists and proud of it)
(and while most of what we make for our own mutual consumption
of durable goods are handcrafted one of a kinds, we do make some
pretty darn cool little trains and agricultural and construction robots
all with sustainable environmentaly friendly clean sources of energy)