The British Library's collection of digitized MSs is an excellent place for finding inspiration, but I used to find finding the right search engine enormously difficult, until I finally went ahead and bookmarked it: http://www.bl.uk/catalogues/illuminatedmanuscripts/searchSimple.asp. I generally search "manuscript and images" for "puzzle" to get examples of penwork initials (and other ones come up as well), and I now have an exemplar or two for almost every letter of the alphabet. I'm slowly working my way through them; half the fun is designing a text for each different letter!
While browsing through the list again today, I found an image which made me immediately "Oh, Lindquistringes!":
This is BL MS Harley 3392, f. 1, Italian, 2nd half of the 15th C. Just change the circle and the Q into a dragon with a gem, and you've got a perfect Lindquistringes design!