Scarcity still wouldn't keep legal items from being indexed online, would it?
Remember that you don't have a global internet in Shadowrun, it's a collection of local matrices, so if the item you're looking for is out of stock with the suppliers on that particular matrix I can see it being removed from any index.
There is a global internet, it's the public grid. Googling still exists, as in page 222 of the core book. There are also other global grids. Plus you can see and visit any host from literally anywhere in the world, from any grid. If you really want an HK-227 submachine gun, and for some reason can't find one with two seconds of googling (which is pretty preposterous IMO), then you can just go to a Heckler & Koch host that will happily direct you a product listing and encourage you to buy it along with all the accessories, ammo, advertisements, and subscriptions your budget can hold. That is exactly what the corps want to happen.
If an item is out of stock, the supplier would still lists it, but with some red text reading "out of stock". And then you can probably just contact them and ask "Hey I really want that R6 bug scanner, can I like preorder it or something so I get it when it's back in stock?", and they will be delighted to let you buy it as soon as they get more. Or chances are you can literally go to the next link that comes up on google and find someone who still has some for sale.
I guess if you're looking for a truly obscure item, then a matrix search test might be appropriate to locate an online listing. But if an individual or organization is on the matrix actively attempting to sell this thing, then that vendor is going to make it as easy as possible for you to find their wares. I'd call it threshold 1 matrix search, and include any applicable penalties (-1 for "intricate/specialized", -2 for obscure, -2 for on another grid).
I think we have differing interpretations of what a Public Grid is. I've taken the information on p. 220 to mean that you will always have access to a grid, one that is provided by "underfunded non-profits, outdated satellites, and the occasional good Samaritan who’s willing to share a wireless access point or two". Yes, you can hop onto the Public Grid from anywhere in the world, but that doesn't mean you have access to every Host, indeed it's specifically mentioned there are Hosts who do not allow Public Grid Connections.
If there are Hosts that detect you're on a Public Grid and so refuse to allow a connection, they won't return a response on a "Google" search, will they?
As for Megacorporations actively looking to sell their goods, it's highly unlikely you buy from the Megacorporation in the first place. If you want a Nuke-It Burrito you buy it from your local Stuffer Shack, not Aztechnology. If you want an HK227 you look for Weapons World, not Saeder-Krupp. And if you're using Ares' Global Grid it won't list the HK227 at all, but will return a listing for the Sigma-3 instead.
This is how I've interpreted the Matrix, and I fully accept it may not have been the intent, but it works. If you want to go with the internet existing prior to 2012 and then being maintained through the various crashes then go for it, it's your game.