Take 1E-13 solar masse as target regime. Einstein radius is 3E=7 smaller than solar mass MACHO.
Quasar ulensing paper from Kochanik has this table:
Lens R_e is for 0.3 solar masses. We are down by sqrt(1E-13/0.2) = 5 e-7. So for a favorable source, lowest mass lensed QSO, we have R_e=7.8e9 cm, and Rs=2e12. Ouch.
We need a more compact source. So use lensed SNe! Typical timescale is dominated by lens motion not source motion, and is 10 years * 5e-7 = 5e-6 yers x 3e7 sec/year = 150 sec.
Now we need an estimate of event rate. Note that apparent angular size is increased by lensed magnification so we don't want highly magnified lensed SNe.