I have LDO TPS70933DBVT (3.3V 150-mA, 30-V, 1-µA IQ Voltage Regulators with Enable). Probably I can use this as constant current source?
I have precision shunt voltage reference TS4061BILT-1.225 (1.225V 0.2%). Another constant current source candidate?
The first part implies 3.3V drop, which is a bit too much. Also, it, in theory, needs output capacitor for stability, although I checked a few mos ldos in the past as current sources, they worked fine without capacitors. You can try... Just check with the oscilloscope that it doesn't oscillate. Also, such ldos are not very precise and often drift a lot with temperature. But, again, that's probably fine for a prototype
.
As of the two-terminal shunt voltage reference, it'll probably require extra parts to become a current source sink (like an opamp). I can't think of a simple circuit to turn it into a floating current sink. May be others will help here.
With inamps be careful with limitations of common voltage and output voltage swing. Check the datasheet carefully, or verify performance in a simulator.
PS ref200 is expensive, imho, unless bought from a questionable source.