catalytic convertor aftermarket ?

Took my 99 in for an "A" service today. I was running perfectly but the check engine light came on a few days ago. Paid $350 cdn for the bill and was told that the cat. convertors were plugged. $ 2000 plus to change them.

On the trip home, the vehicle would barely climb two long hills on the highway. Dealers response is that he already told me the problem. I think it is quite a coincidence that it starts to act up a mere ten minutes after leaving the dealership.

Is there anything I can check ? Is there any source of aftermarket convertors ?

Thanks in advance for any help.

allen