I need to buy some Latvian Lats, but the rate here in Vancr is abysmal ($CDN2.40 to buy 1 Lat, at my usually

exchange,
www.vbce.info). Travelex's on line rate looks much better for £ to Lats - saves about $C40 per 50 Lats - if I wait to buy at LHR T4 will the walkup rate be as good, or should I just buy the currency now, then pick it up a a few weeks at LHR?
Have never used Travelex, hence my

at the best way to go about it. Thanks for any and all advice.