I am 99% sure Sierra is all 33-240 ohm, so most standard senders will work. The dual gauge sender will NOT work right with only one gauge hooked up to it!
Moyer sells appropriate senders usually, but they seem out of stock right now. This one from Amazon would do if you need it right now:
https://www.amazon.com/Sierra-18-589...1386259&sr=8-3
Or here:
https://www.fisheriessupply.com/sier...enders-18-5899
You could call Moyer and see if they have any, the website shows sold out.
Defender has these that would work:
https://www.defender.com/product.jsp?id=1566892