See my answer over here. It's not a particularly bad idea to just add dragon magic to the available supply, and you may do it with an evil in sufficient quantity to result in any naturally-occuring result along the spectrum of draconicity for any target including a shren, perhaps even in batches. Permanently fixing the situation to accommodate any growth in the dragon population would require either an edit to how the species works - which would be dangerous, and there aren't any Elcenian unicorns to consult the way there are in Thilanushinyel - or altering the way the magic supply works, so it's rapidly self-regenerating instead of a finite pool.