I see alternative blocks reorganizing the blockchain in monerod, but my mining pool's orphaned block doesnt show.
Orphaned block means that your pool was able to mine a block but somehow someone was able to mine that same block. In the end your block was not chosen thus it became orphaned.
Other nodes that may have added your pool's mined block will have to discard it.
An alternative block could happen if the network is divided and is extending on two different blockchain. This happens because it was not detected that two same block was mined by two separate pool and the network was extending on different blockchain. When the network notices this it will have to reorg and have to select the longest block chain.
Here is a nice answer Block added as alternative on height xxxxx