Can I use cards that search for a Pokemon, like "Bebe's Search" or "Poke Ball" to get a Pokemon LEGEND card from my deck?
Any effect that lets you search your deck or discard pile or do something from your hand with "a Pokemon" will let you use that effect on one half of a Pokemon LEGEND set, but not both halves.
Source: HeartGold & SoulSilver FAQ (2010-02-11), PUI Rules Team (2010-02-11)

Relevant cards

Note: All applicable cards may not be listed below.
WOTCB2_121
WOTCB2_121
BW1_97
BW7_131
DP1_110
DP5_85
EX1_86
EX10_87
EX14_82
EX6_95
G1_67
HGSS1_95
PL1_113
SM1_125
SWSH2_164
SWSH2_164
TK4-Gyarados_23
TK4-Gyarados_23
TK4-Raichu_25
TK4-Raichu_25
TK6-Noivern_21
TK6-Sylveon_26
WOTCJU_64
XY0_35