Reconciliation between gstr2a and gstr3b

input availed and input available in gstr_2a must be the same 

so ask supplier to put the bills in gst returns 

Yes your 2a must be match with Books ,..as while filing GSTR 9 (Annual Return) the ITC is going to be Autopoulate from 2a.

But in my view if you have the Original Invoice & reced the goods for the same , but not reflecting in 2a & inspite of reqular request to supplier about the same the supplier do not get it done , then also you can avail ITC for the said invoice. Because

1. Gstr 2 is not started : able recepient to add the missing bills
2. in Gstr 9 under s.no.6 (a) total itc from 3b will also autopopulate therein & Difference with autopopulate 2a under s.no. 8(A)can be explain therein.

3. In many cases the supplier has shown the bill in his Gstr1 but the same is not reflecting in 2a of recepient

And moreover for fy 2017-18 , Govt will also show some leniency in this regard.

At the time filing Annual Return in GSTR9 Under SL.No.6(a) Shows Total ITC from GSTR3B on Autopopulate and Difference Displayed GSTR2A Under SL No.8(a).Then You can correctly explained the difference.