Honestly, the majority, if not ALL the Rin cosplayers I see at the local big con here, are not with a Len either lol Most of them are with other Vocaloids, but no Len lol and worse, all the dang Len's are alone for some reason haha I think you will be just fine. If you are signed up for the forums on you're con's site (provided they have them), some con forums have a "looking for ____ cosplayer" thread. You could ask there if you can and maybe get lucky and find a lonely Len.
Cosplay DA Regular DA
-Fate Testarossa (Mahou Shojo Lyrical Nanoha A's) ~90%-
-Ryouko Ookami (Ookami san and her 7 companions) ~75%
-Amy Sorel (Soul Calibur) 25%-