To get HM7 (Waterfall) in Platinum you can get it at Sunyshore City talking to Jasmine at the north of the city.
Chat with our AI personalities
The HM Whirlpool is not obtainable in Pokemon Platinum, for there is no use for it during gameplay.
Dig is not a HM in Pokemon Platinum but a TM, it can be found in the ruin maniacs cave.
In Pokemon Platinum, Flash is a TM.
Surf is HM #3. :-)
at the city of the Pokemon league