To obtain probes you will have to buy them in the fuel tank, each one has a price of 20 credits. You will have to buy again after the ones you have been filled enough, although you should bear in mind that initially your boat only has capacity for 30 probes, so you will have to be checking the fuel tank with some frequency. You can increase its capacity to carry up to 60 probes.
To increase the capacity of your ship, you will need to have Thane on board, so you will have to complete the Dossier: the assassin's mission.
With Thane on the ship, you must go with him to find out in what ways you can improve the ship. Thane will give you ideas, and you will have to select "yes" to improve the ship, which will allow you to access the update interface where the modular probe bay is in the ship updates option, but you will need 15,000 iridium to update the probe capacity.
That's all you have to know about how to get probes in Mass Effect Legendary Edition, we hope that now that you know how to get and how to improve their ability, you can get a lot of alien techs with our recommendations.