can u give the equivalent for 2N4392 JFET and its datasheet

Why? 2N4392 is an in-production part available e.g. from Centralsemi and Interfet. If you want to search a similar part from the parts available at your local shop, compare Vgs(off) and Idss.

2N4392 is available from Mouser (in multiple countries):
http://www2.mouser.com/Search/Refine...Keyword=2n4392

Better than 2N4392 is 2N4391 which have rDSon = 30ohms vs 60ohms.

One of the best switching JFETs on the market is 2N5432 (rDSon = 5ohms, Igate=100mA)
http://www2.mouser.com/Search/Refine...Keyword=2n5432

but i failed to get 2N4392...can u give its equivalnt

hey,is 2N4392 available in ordinary electronic shopss?else from where will I get it?

What do you mean ordinary electronic shop?
Mouser have dealers in about 60 countries all over the world. Check if your country is in the list:

http://www2.mouser.com/localsites/

I don't know exactly your application, but sometimes there is a possibility to place up to 3 JFETs in parallel (one in top of each other) to increase the performances, as lowering rDSon and increase the gate current.
This is one advantage of JFETs compared to BJTs. For BJTs, to use in parallel have to use ballast resistors.
For this you can use cheap JFETs as J310 or BF245C.

its for making a beacon transmitter

OK. Up to 450MHz you can place 3 x J310 (or BF245C) in parallel to increase the power.