The pants shown above are the Shardling Legguards from Heroic Halls of Stone, from the giant Krystallus. You can buy wow gold and get a perfectly good alternative from the Argent Crusade at Honored reputation, the Standard Issue Legguards. The socket is blue instead of red, and the Haste is only about half of the Shardling Legguards, but it's a Level 78 item and it's fairly easy to get to Honored with the Argent Crusade if you level through Zul'drak and open up Crusader's Pinnacle in Icecrown.

There are no blue Haste plate boots in Northrend, but the red socketed Mojo Frenzy Greaves from Moorabi in Heroic Gundrak should do nicely. Since you're doing Gundrak, or if you can't do the heroic version yet, make sure you're on the quest One of a Kind, where you need to get that item that's spherical, but quite pointy at parts. You can get the Slippers of the Mojo Dojo, which has no socket but it'll do. Blacksmiths can easily craft buy wow gold  Ornate Saronite Walkers and Brilliant Saronite Boots, both of which use up twelve Saronite Bars, with the former using an extra Eternal Shadow. The Ornate one will complete your look, but the Brilliant treads will be better for dungeons.

There are two excellent options for the wrist slot for Haste, both relatively easy to obtain. The first are the Bands of Fading Light, another pair of BoE cuffs that should be relatively affordable in the new economy. The Bands are a zone drop from Heroic Utgarde Pinnacle, which should give you more reason to go in addition to the head and shoulder pieces. If these don't drop for you or you don't manage to find it for sale, you can grind to Honored with the Wyrmrest Accord for the Bracers of Accorded Courtesy, which have a yellow slot instead of a blue one, with more Haste as a socket bonus. It's wearable at Level 78, and you should reach Honored with the Accord by questing in Dragonblight and Coldarra.

I know I've been advising a lot of trips to the Auction House, and this pair of gloves is no exception. It's the only pair of rare Haste Plate in Northrend, but since the Web Winder Gloves drop buy wow gold  all throughout the continent, it should make its way into the market quite often. If you don't manage to snag a pair of these, there are decent alternatives with Critical Strike Rating instead, some of which can be crafted by Blacksmiths.