FAIR TRADESMagmar

Some Pokémon can only be aquired through trading, as much as I hate to admit it. Here's a list of what each version needs from the other, as well as the four Pokémon you can only obtain by trading.
POKÉMON
VERSION
MUST TRADE
23) Ekans
Red
-
43) Oddish
Red
-
56) Mankey
Red
-
58) Growlithe
Red
-
123) Scyther
Red
-
125) Electabuzz
Red
-
27) Sandshrew
Blue
-
37) Vulpix
Blue
-
52) Meowth
Blue
-
69) Bellsprout
Blue
-
126) Magmar
Blue
-
127) Pinsir
Blue
-
83) Farfetch'd
Both
21) Spearow
108) Lickitung
Both
81) Slowbro
122) Mr.Mime
Both
63) Abra
124) Jynx
Both
61) Poliwhirl
YELLOW TRADES

Here are the Pokémon that you'll need to trade for if you have the Yellow version. Don't say it's not fair; I know.
POKÉMON
VERSION
MUST TRADE
13) Weedle
Either
-
14) Kakuna
Either
-
15) Beedrill
Either
-
23) Ekans
Red
-
24) Arbok
Red
-
52) Meowth
Blue
-
53) Persian
Blue
-
109) Koffing
Either
-
110) Weezing
Either
-
124) Jynx
Either
-
125) Electabuzz
Red
-
126) Magmar
Blue
-
122) Mr.Mime
All
35) Clefairy
67) Machoke
All
104) Cubone
51) Dugtrio
All
108) Lickitung
47) Parasect
All
114) Tangela
112) Rhydon
All
55) Golduck
87) Dewgong
All
58) Growlithe
89) Muk
All
115) Kangaskhan
The Story
Beginning tips
Cheats
Pick a starting Pokémon
TMs
RBY TM chart Part 1 Part 2
Gym Leaders
Attacks 1 2
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Level skills- Part 1 Part 2
Pokémon Stats- 1 2
Locator- By Locations By Pokémon
Evolutions
Trades
Who's the best?
Battle Games
Gameshark Summons Items and Skills
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TV Show
Beat This!
THE JOHTO FILES
STADIUM I Tips Gym Leader Castle Pika Cup Petit Cup