Strings for Fanned Fret/Multiscale

There are strings made specifically for those basses. The manufacturer will have a list of sets that will fit.

 

Instead of using the search function within this forum (which is not very functional), try doing a general Google search by entering "talkbass followed by the subject matter".

 

Multi-Scale Fanned Fret Bass Strings from Bass Strings Online

 

You can ask @HaphAsSard , who is quite knowledgeable on things like this.

 

Comiiing!
At first I got nothing, but Google is indeed my friend (and I do know one or two tricks to navigate the vastity of the cyberocean as it pertains to strings and Europe)...

1a) First off, a couple Euro websites have multiscale-specific products available (Dingwall and Payson):
Musik Produktiv
Dingwall Bass Strings, Payson, Nickel, Stainless Steel , Groundwound:: For sale, UK, Eu, On offer, Basses Guitars Accessories at Bass Direct: Bass Guitar Strings -

2) Then, a useful post by a more knowledgeable user than myself:
Strings For My Fanned Fret Bass
with the caveat that it only partially applies to your case. The post and the thread refer to an Ibanez model with a shorter overall scale...fanning (35.5" to 34"). However, if you're interested in a 4-string Dingwall tuned drop B like in your current setup, the 36.25" scale of the lowest string would allow you too, just as it does that Ibanez owner, to use commonly-available super-long/extra-long (or however companies choose to call them) sets by many companies, not just those which make fanned-fret specific sets or "very long scale" in La Bella's case. Here are some of the biggest Europe-based online string vendors:
Gitarrensaiten - Plektrum - Kapodaster - Gitarrenzubehr - Saiten
Lord of the Strings
Online Guitar Strings and Accessories
SAITEN im SAITENshop kaufen bei SchneiderMusik.de
and of course the usual general-purpose stores:
Welcome - Thomann International
Bax Music | We support your stage
Musik Produktiv Online-Shop - Buy music instruments online. (already linked to above)
I've never checked MusicStore.de or DV247 for strings, but there's them as well.

1b) Speaking of La Bella, some UK online stores carry their products and should/might be able to order any type in very-long size for you:
ELECTRO MUSIC - The Independent Music Store | UK
http://www.stringbusters.com/Ko-Bespoke/productlist.asp?cat=1/BASS STRINGS/BASS STRINGS LA BELLA
and the aforementioned
LaBella strings
This, in case you are after a 5-string Dingwall, in which case common super/extra long scale might not work (you need at the very least 37" + about 1" from ball-end anchoring to saddle, and not all super-longs would certainly clear the nut - check here which do and which don't, courtesy of the upthread-linked Bass Strings Online), and in case you're not satisfied with Dingwall-branded or Payson strings for whatever reason and wanna check out La Bella as well.

3) Finally, Pyramid will probably make everything they do in whatever custom length you want:
PYRAMID maximum performance strings - Sonderanfertigungen, Custom Shop, Custom Strings, Instrumentensaiten Bestellservice
(Sending an email should suffice if you don't feel like using their German language order form).

 

Payson would get my vote.

 

Update - Pyramid already make multiscale sets (page 35 of their online catalogue).