The big bummer here is that Honda has a very limited number of connectors that they sell separately. Those connectors are typically for items like headlight, taillight, marker lights. If you need a connector outside this scope the only real option is to buy a complete harness.
To clarify the differences.
08W18-TR0-100 - 2012/2013 Civics and designed for use with in-wheel TPMS. 18x7
08W18-TR0-100B - 2014+ Civic with indirect TPMS, 18x7
08W18-TR0-100A - 2014+ Civic Si with indirect TPMS, 18x7.5