Dextran is available in a variety of molecular weight ranges. It can be conjugated with Cascade Blue very easily by the method described in this paper:
Analytical Biochemistry Volume 198, Issue 1, October 1991, Pages 119-130
Cascade Blue derivatives: Water soluble, reactive, Blue emission dyes evaluated as fluorescent labels and tracers
James E. Whitaker, Rosaria P. Haugland, Patrick L. Moore, Peter C. Hewitt, Ming Reese, Richard P. Haugland