I emailed the seller yesterday, asking her if she had a set with a red and a brindle cardigan (and tried to gently point out she might have trouble selling the brindle and merle pems.) Just in case anyone is interested, here is her response:
Thank you for your question
Of course, I have a set of shakers with red cardigan and brindle cardigan because I can paint every color of cardigan corgi.
You can buy this set of cardigan and I will send you a set of shakers with red cardigan and brindle cardigan to you.
Please leave a note when you check out that what color of cardigan that you want.
Thanks and Regards