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
Kumoricon 2014 (so far):
-Sora (Kingdom Hearts 2)
-Alice (Hearts no Kuni no Alice)
-Black&Blue Loli-style Dark Magical Girl O.C.
-Akaito (Vocaloid. Black & Red Ver.)
Dream cosplays for now:
-Tsuruya-san (Haruhi Suzumiya)
-Kagami Hiiragi (Lucky Star)