Geriye dönük olarak dolar kurunu TCMB sitesinden parse eder.

parse.php

<?php
/* @barisesen
 * http://www.tcmb.gov.tr/kurlar/201805/25052018.xml
 */
public function oldExchangeRate($date)
{
    $dt = Carbon::parse($date);
    if ($dt->isWeekend()) {
        return $this->oldExchangeRate($dt->subDay());
    }

    $year = $dt->year;
    $month = $dt->month < 10 ? "0{$dt->month}" : $dt->month;
    $day = $dt->day < 10 ? "0{$dt->day}" : $dt->day;

    if (Cache::store('redis')->has("{$year}{$month}{$day}_USD")) {
        return Cache::store('redis')->get("{$year}{$month}{$day}_USD");
    }

    try {
        $site = $this->request("http://www.tcmb.gov.tr/kurlar/{$year}{$month}/{$day}{$month}{$year}.xml");
        $data = simplexml_load_string($site);
        $dolar = ['selling' => (string)$data->Currency[0]->ForexSelling[0], 'date' => (string) Carbon::now()];
        Cache::store('redis')->put("{$year}{$month}{$day}_USD", $dolar , 24 * 60);
        return $dolar;
    } catch (Exception $e) {
        // resmi tatil günlerinde kayıt olmadığı için hata döner. Bu durumda bir önceki günün kuruna bakabiliriz.
        return $this->oldExchangeRate($dt->subDay());
    }
}

request.php

<?php

public function request($url)
{
    $ch = curl_init();

    curl_setopt($ch, CURLOPT_REFERER, 'http://www.google.com');
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    $response = curl_exec($ch);
    if (curl_error($ch)) {
        throw new Exception("{$url} adresinden doviz kuru alinamadi!");
    }
    curl_close($ch);

    return $response;
}