From what I can gather, the part number for the SX135 fuel tank is UP00136A. PartsTree can get the part, but it's not a stocking part and I think we have our website setup to not accept orders containing Homelite parts at this time. Here's a couple of websites that do offer them:
$23.80 - http://www.amazon.com/dp/B000PLVG7U/...U&linkCode=asn
$20.40 - http://www.cmsmallengines.net/yard-broom-c314.html
$20.40 - http://www.m-and-d.com/HM-UP00136A.html
If these guys can't get you what you need let me know and I'll see what I can do.