Season 4-5 ever released separately on DVD?

The prices for this show are ridiculous. I have seasons 1-3 but cannot get the season 4-5 5 disc set. It is on BigW website but "unavailable". No copies on Ebay. Saw one site that had the whole set that sold for $147!!!! Friggin unbelievable. Did Roadshow actually release the season 4-5 set? Am thinking it was never sold separately but bundled with the whole series in a limited release. That at least would explain why this series seems to have reached "collectible" status with accompanying exorbitant price tag.