Since the TM251 is a Mcculloch, it shares the t25 (or p25) type head with other husqvarna subsidiaries - Partner, Weedeater brands I have also got that head on.
Just type "Mcculloch 25 head" into google and you will see plenty of whole heads for sale for the $15-20 dollar mark. Keep the old one for spares
Since I am not a massive fan of them (though they are by all means not the worst I have used), and would highly suggest throwing on a speed feed head off ebay.
Note - although SF heads come with many adaptors, none seem to fit Mcculloch.
The best way I have found is to take the steel nut out of the old T25 head and grind the top thin 'spout' off the top, and take a little off each hexagon face.
But for god sake dont cut it with an angle grinder if its aluminium adaptor (which some are)
