In The Elder Scrolls IV: Oblivion (including Oblivion Remastered), shops restock their inventory approximately every 48 to 72 in-game hours. To restock a merchant's items, you need to:

• Buy everything you want from the shop.
• Leave the shop building and fast travel to a different location, ideally in another town or city.
• Wait for about 48 to 72 in-game hours (usually waiting 24 hours three times or 48 hours twice works).
• Avoid visiting the shop or its area during this waiting period.
• After the waiting time, return to the shop, and the merchant's inventory will be fully refreshed with new goods and replenished gold.

This method works for all types of items, including ingredients, potions, lockpicks, and enchanted weapons. The waiting can be done using the in-game wait function, and it is important to be outside the shop when waiting to avoid glitches

. In summary, shops restock roughly every 2 to 3 days of in-game time, and you can speed up the process by fast traveling away and waiting before returning to the merchant