Can I get Avamar backup solution alone without data domain storage? 

Avamar system has two logical components: the Avamar Administrator Server which runs on the Utility Node and Avamar Data Server. Your question is about Data Server. As a Data Server, you can use Data Domain or Avamar GSAN which is a set of Avamar Storage Nodes (computers with internal disk drives) running as a grid. This is native Avamar solution but has limits for the number of SN and the total capacity of GSAN grid. The better of these is Data Domain, but to answer your question: you don't need DD, you can use GSAN grid.

No it supports only Data domain as a integration , for extended data retention , you can use emc networker as a media sever to configure the backup to tape