https://www.thomann.de/gb/rockbag_warlock_bassgigbag.htm
https://www.andertons.co.uk/bass-dept/bass-guitar-strings-accessories/cases-bags-for-bass-guitars/gig-bags-for-bass-guitars/bc-rich-premium-bass-guitar-gig-bag-mockingbird-warlock
That's all I can come up with a quick google. Out of stock, naturally, probably need to be special ordered, because they're so niche. These may seem expensive to you, I don't know what your definition of £'ssss is. Welcome to the world of odd sized gig bags. Having owned a few Thunderbirds and Jack Casadies, I can sympathise.
Good luck.