Lots of ways to stop the awning sliding. If you always slide ON in one direction, a very descrete bend in the awning rail will stop the other end. You can also "thread" a large bolt to fit the rail after the awning is in place. It should be easy to unscrew by hand.
Took a look myself, I see what you mean, ouch! $20 a pair on eBay. Only listings are from UK. If it were me, I'd spend $12 in material and the better half of an afternoon making a pair (oh ya, lets add up the savings there! )
Seriously, there's got to be something one could use in place of those. hmmm
We never really grow up, we only learn how to act in public. '12 Weakender TD (homebilt)(43 States & almost 35k miles) '67 Shasta Compact '67 Bee Line Wasp