vorrätig
in stock
Available in a warehouse or store and ready immediately. Something is in stock and can be bought or used.
Haben Sie dieses T-Shirt auch in Größe L vorrätig?
Do you also have this T-shirt in size L in stock?

in stock
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in stock
Available in a warehouse or store and ready immediately. Something is in stock and can be bought or used.
Haben Sie dieses T-Shirt auch in Größe L vorrätig?
Do you also have this T-shirt in size L in stock?

The adjective 'vorrätig' (in stock) is derived from the noun 'der Vorrat' (supply/stock). A 'Vorrat' is a quantity of things that you keep for the future. So when something is 'vorrätig', it is available from this supply.
Wir haben noch einen großen Vorrat an Nudeln im Keller.
We still have a large supply of pasta in the basement.
'Vorrätig' (in stock) is almost always used predicatively with the verbs 'sein' (to be) or 'haben' (to have). An attributive use such as 'das vorrätige Hemd' (the shirt in stock) is very rare and sounds unnatural.
Leider ist das Medikament zurzeit nicht vorrätig.
Unfortunately, the medication is currently not in stock.
You hear this word very often when shopping, in stores, pharmacies, or restaurants. It is the typical answer to the question of whether a particular item is available.
Entschuldigung, ist dieser Pullover auch in Blau vorrätig?
Excuse me, is this sweater also in stock in blue?
available / present
'vorhanden' and 'vorrätig' both mean that something is there and available. 'vorhanden' is more general and can fit many things: information, rooms, devices, or money. 'vorrätig' is used especially in shops, warehouses, or pharmacies. It means that something is in stock and can be bought or used immediately. Learners easily confuse the words because both mean 'there'. When it is about goods or inventory, 'vorrätig' is more precise. In other situations, 'vorhanden' is more natural.

Das Waschmittel ist im Supermarkt wieder vorrätig.
The laundry detergent is back in stock at the supermarket.
Im Bus ist leider kein freier Sitzplatz mehr vorhanden.
Unfortunately, there are no free seats available on the bus anymore.