Is there a list that shows how many pocketmons there are or were as of each generation?
Like 151 in 1, about 250 in 2, and so on?
Game Freak doesn't internally separate things by Generation, its a fan-made division of games, so I will list all of the times the National Dex has increased in size, since starting in what fans refer to as "Gen VII" new Pokemon get added almost every game. I'll list how big the National dex was on the release day of each new game, note that from Let's Go onwards there are no games that have all of the Pokemon listed:
Red/Green/Blue/Yellow: 151
Gold/Silver/Crystal: 251 (+100)
Ruby/Sapphire/Fire Red/Leaf Green/Emerald: 386 (+135)
Diamond/Pearl/Platinum/Heart Gold/Soul Silver: 493 (+107)
Black/White/Black2/White2: 649 (+156)
X/Y/Omega Ruby/Alpha Sapphire: 721 (+72)
Sun/Moon: 802 (+81)
Ultra Sun/Ultra Moon: 807 (+5)
Let's Go Pikachu/Let's Go Eevee: 809 (+2)
Sword/Shield(Base Version): 890 (+81)
Sword/Shield(Isle of Armor Update): 893 (+3)
Sword/Shield(Crown Tundra Update)/Brilliant Diamond/Shining Pearl: 898 (+5)
Legends: Arceus: 905 (+7)
We currently know about three Pokemon that are going to be in Scarlet and Violet, so in terms of entirely unique species there are 908 revealed to the public as of this post,.