Tomb king morghast blades. They're definitely big enough, have a wraithbone feel and look very dark kin (jagged and ornate).
I have use them as close combat weapons for my kit-bashed taloi and grotesques, so I'm not sure exactly how they'd marry to the newer incubi models. The blades are 4.5 cm long from tip to tip, 0.5cm wide except where they flare out, and very modifable.
They also look pretty darn cool.
From bits dealers on ebay you can get them for about $1 a piece, although I got lucky and scored a couple dozen in a random $5 bit box.
http://www.ebay.com/itm/WARHAMMER-BITS-TOMB-KINGS-VAMPIRE-COUNTS-MORGHAST-ARCHAI-HALBERDS-/351356947985?pt=LH_DefaultDomain_0&hash=item51ce818e11