Thyristor latching problem
Assuming you mean an SCR you can use a parametric search at a distributor to find parts with low holding current.. eg. TS110-7 2mA maximum. You can minimize it by keeping the gate-cathode resistance relatively large. 

There are thyristors with much lower holding current (eg. 2N6028) but they are not going to work without a lot of modifications to your circuit. 

Or just connect two transistors as a thyristor. The value of the emitter-base resistor(s) will determine the holding current and you can make those resistors very high value.







simulate this circuit &ndash; Schematic created using CircuitLab

Here you can see that it typically holds at &lt; 100uA.