William Dam Seeds has a newer variety called Guelph Millenium at $11.50 for 10 plants, plus shipping. You could also try Stokes or Veseys. Richter's is a great place for unusual herbs and plants, but for good 'ol asparagus, you can probably buy it cheaper elsewhere. My personal recommendation is to wait until early spring and buy the roots "fresh" from your local plant centre. You can check the roots and only buy the ones in good condition and there will be no shipping fee. Plus, you can plant them as soon as you get home.

Here is a link that might be useful: William Dam Seeds asparagus plants