Is there a master link for single speed chain that will fit in Shimano chain tensioner?
Assuming you have a new KMC chain (pic of the connector is KMC).

KMC definitely makes 1/8" chain connectors of the 'Missing Link' style without the extra side plate clip that is presumably causing problems. 

See here: http://kmcchain.us/connectortype/single-speed-ml/

and here: http://www.kmcchain.eu/connector-bmx_track_fixie

Can't tell you if those are readily available in Russia or where the best place to buy them is.