Dragon Scarf - Yarn Substitution Suggestions?

New poster:

I'm planning to make the Dragon Scarf (don't have my book here to type in the exact name, sorry!) and was wondering a bit about making yarn substitutions.

I'm having trouble finding all the colors in a DK yarn that I like working with; would it be better to go down to, say, sport-weight and double-strand or to go up to worsted and accept that the scarf will be slightly misproportioned because of it?

Thanks!