I'm thinking about brewing a barleywine. A recipe that looks interesting to me uses Magnum and Horizon hops, but I don't have access to either at my (small) local brewing store. What are some good high-alpha alternatives for a barleywine?
I always use this hop substitution chart, but there are others available too. According to it, Horizon and Newport are substitutions for Magnum.
Galena, Nugget, and Fuggle are substitutions for Newport, so you could try that too.
Finally, it lists Magnum as a substitute for Columbus, which might be easier to find.
The BYO chart suggests Northern Brewer.
Ultimately, for a barleywine I think you'll be happy with any of those, as the style doesn't feature hops. You're mainly using the hops to balance the barleywine.
Magnum and Columbus hops produce very different results. Magnum is a low cohumulone hop, which results in a very smooth bitterness. Columbus is relatively high cohumulone and will give a much sharper bitterness. Horizon is my usual sub for Magnum. As to a BW not featuring hops, it really depends on what style of BW you're making. English BW are subdued on the hops, but Am. styles are very hop forward, often running to 130 IBU with very prominent hop flavor and aroma.