My LHBS said that Victory or Biscuit are good substitutes. Looking at the Northern Brewer Catalog their Crisp Amber malt is 27L. The Briess victory is also 27L and the Belgian biscuit malt id 24L.
Crisp Amber - Warm, pleasant, biscuit flavor with coffee undertones
Briess Victory -This exceptional malt delivers truly unique biscuity, nutty flavors. Well suited for Nut Brown Ales & other dark beers. Its clean flavor makes it well suited for ales and lagers alike. Use in small amounts to add complexity to lighter colored ales and lagers.
Biscuit is a highly kilned character malt that adds a wonderful toasted nut flavor and aromas to the beer. A bit more intense than Aromatic malt so do not use more than 5% in your recipe.
I think either is good but I went with Biscuit for my DFH Shelter Pale Ale