Parth's suggestions are good but don't answer your question exactly since they don't allow you to insert characters using only the keyboard.
Your keyboard may not have a number pad as such; most laptops don't. But look at the JKL, UIO etc keys. Do they have small numbers on them? If so, it's what they call an "embedded number pad". Usually you use some combination of NumLock and the Function
key to enable it. Once you've done that, you can use ALT + the embedded number keys to enter special characters.
Clumsy, but it works.
More work but way less clumsy:
Add the characters you need to PPT's Autocorrect settings. For example, A with accent grave:
Use the insert symbol or the windows Character Map app to locate the correct character, copy and paste it into a text box in PPT.
Select and copy it.
Go to File | Options | Proofing
Click AutoCorrect Options then choose the AutoCorrect tab.
Under "Replace:" type Agrave
Under "With:" click in the text box then Ctrl+V to paste the previously copied A with accent grave character.
OK the dialog box and get back to PPT.
Now, when you type Agrave followed by a space character, AutoCorrect will replace it with the actual character.
In this example, I'd do both Agrave and agrave, one for the uppercase A, the other for lowercase.
Or to make it easier to find all of your corrections in the list, you might want to use something like <<Agrave and <<agrave
Tedious to set up, simple to use later.
Now does anybody know where PPT stores the autocorrect entries so you can back this baby up once it's created?