What got me wondering about this was a shopping list. 7 different items. All with availability at a level that meant I'd hit it on my first roll. And all over 100 in cost.

And that's when I realized that just going shopping was going to take longer than my last mission. I've got to be misunderstanding something, but what? Should shopping list be gotten through contacts? Does the guy with the Sound Suppressor have other mods but I have to come back tomorrow?

I could go with the thought that it's all custom made. If so, I'd like the guy who made my Sound Suppressor to install it while he's at it.

If it's handwave/GM's call, that's cool. I can run with it. But if there is a rule in the books involving doing a lot of long interval tasks, I'd appreciate a point to it.

I don't know of any RAW on the subject, but the most reasonable solution I've heard is to make one test against the item with the highest availability rating.

Or at least group them together by type or contact.

My ruling would be something like anything of the same type with availability under 12 can be rolled as a group at the highest availability with a dice pool penalty of -1 die per additional item. No reason why your Talismonger would also have a suppressor for an LMG, for example.

This, of course, does not apply to any items that may be purchased legally.

I envision buying as going from merchant-to-merchant, asking where you can get what you're looking for. A good roll means a merchant points you towards someone who can help you. A bad roll means the merchant don't have a clue where you'd get your product. If you're buying 7 items, there's no reason you couldn't ask the same merchant 7 questions in one conversation. The time period between rolls is the time it takes before you can meet the next merchant. An item requiring weekly rolls means that you have to make appointments with merchants a week in advance.

If you have a time limit, say 2 days to find a bunch of items with a purchase period of 12 hours, make four Charisma + Negotiation tests. You can purchase all items with an availability equal to or less than your total hits.

The GM may make you roll separately for distinctly different products that would be sold through different merchants, eg. fancy clothes and military drones.

Split the dice pool like it was ambidexterity if you want it limited.
To have it less limited use it like burst fire using the highest avail +1 for each item of at least half that value.

Its generally easier to restrict income than availability.