Yes. Try the H11F1 optoFET. That can vary from >300 Mohms down to a few
tens of ohms or less, when its LED is fed by an input voltage via a series
resistor. I haven't yet tried it for linearity, but it's a nice idea
because it isolates input and output. If you use the output to drive
another FET, you can probably arrange a near-zero ohms to >300 Mohms
resistor.
I just got an email 2 days ago that says the H11F1 was just announced as
discontinued:
"You have purchased the following part number(s) from Digi-Key within
the last two years. The manufacturer has announced this part(s) will
become obsolete. Please click on the link below for more information on
possible substitutes.
FAIRCHILD OPTOELECTRONICS GROUP
Description: OPTOCOUPLER FET BILAT 6-DIP
Manufacturer Part Number: H11F1
Digi-Key Part Number: H11F1-ND"